WASHINGTON (AP) — The latest developments in the 2016 campaign for the presidency. All times EDT:

4:18 p.m.

Hillary Clinton is hitting another campaign milestone: Most retweeted tweet.

"Delete your account," her campaign wrote, in response to a message from Donald Trump mocking President Barack Obama's endorsement of the presumptive Democratic nominee on Thursday.

The message quickly went viral, getting retweeted 130,000 times in about an hour. "Delete your account" is a typical joke used on the social media site, often deployed when someone has failed to be funny.

Trump, who's known for his brash voice on the site, has 8.76 million followers to Clinton's 6.6 million.

The exchange prompted reactions from across the political spectrum.

"If anyone knows how to use a delete key, it's you," replied Reince Priebus, chairman of the Republican National Committee, in a reference to the messages Clinton deleted from the private server she used for her correspondence at the State Department.

Former New York Rep. Anthony Weiner also weighed in, tweeting: "Too late to for some of us." Weiner resigned his seat in Congress after sexual messages he sent over the social media site became public.

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Sen. Chuck Schumer says Bernie Sanders is doing just fine, even as endorsements pile up behind presumptive Democratic presidential nominee Hillary Clinton.

The New York Democrat says Sanders, who has not quit the race with Clinton, is " not worn down, he's not bitter, he's not angry, I told him I was proud of him and what he accomplished." Schumer spoke after a meeting with Sanders, who is touring Washington's Democratic power brokers Thursday.

Schumer, the Senate's No. 3 Democrat, added that Sanders "cares a lot about the Senate majority becoming Democratic, but he also cares about keeping his people engaged. "

On "so many issues," Schumer said, Democratic senators and Sanders, an independent, "are aligned."

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4:17 p.m.

He's not worn down, he's not bitter, he's not angry, I told him I was proud of him and what he accomplished," Sen. Chuck Schumer said after meeting with Sanders.

"He wants to make sure that the issues he's pushed for have vitality and help us get those things enacted. He cares a lot about the Senate majority becoming Democratic, but he also cares about keeping his people engaged, and the way to do that is issues," Schumer said. "On issues, on so many issues, the Democratic caucus and Bernie Sanders are aligned, so I think we're going to have a great, constructive relationship, I think Bernie will be constructive throughout."

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3:36 p.m.

Several uncommitted Democratic superdelegates are still waiting by the phone for calls from the Democratic presidential candidates — even though Hillary Clinton has claimed the nomination, President Barack Obama has endorsed her and Bernie Sanders is taking meetings around Washington with party luminaries who expect him to quit the race at some point.

Rachel Binah of California says she has made it clear publicly that she wished to hear more from both candidates about their plans on safeguarding the environment, such as permanent protection of oceans from offshore oil development. She said Thursday she had not heard from the Sanders campaign and hoped to hear from the Clinton campaign soon.

"I am still waiting," Binah said.

Superdelegates are Democratic Party leaders like governors and members of Congress, who can vote for any candidate at the national convention. Clinton holds an overwhelming lead among superdelegates who have committed to one candidate.

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3:13 p.m.

Senate Minority Leader Harry Reid says he thinks Bernie Sanders has accepted the fact that Hillary Clinton is the presumptive Democratic presidential nominee.

Reid met with the Vermont independent senator at the Capitol on Thursday. Reid told reporters after the meeting that he was in a good place with Sanders and Sanders is in a good place with the Senate Democratic caucus.

Reid said he has invited Sanders to speak to the caucus next week. The Nevada Democrat spoke about how he admires Sanders vigor and reflected upon the battles they've fought together.

"I didn't hear a single word about him trying to change the fact that she's the nominee. I think he's accepted that," Reid said.

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3:00 p.m.

Former Democratic presidential candidate Martin O'Malley has endorsed Hillary Clinton.

The former Maryland governor and Baltimore mayor announced his support for Clinton Thursday. "I am committing my energies to the election of Secretary Clinton," he said in a statement. "The stakes in this election could not be higher, and the choice is clear."

Clinton declared victory over rival Bernie Sanders on Tuesday, having captured the number of delegates needed to become the first female nominee from a major party.

O'Malley suspended his campaign for the nomination after a distant third-place finish in Iowa.

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2:42 p.m.

Paul Manafort, Donald Trump's chief strategist, is saying the presumptive Republican presidential nominee's campaign's fundraising operation will generate "enough to win."

Manafort, speaking briefly after a meeting of GOP donors in Manhattan on Thursday, declined to state a fundraising goal. But he said that "we'll raise what we need to raise" and suggested that the amount of money needed to win in November will not be "be as much as people think."

Trump had originally suggested he wanted to raise $1 billion for the campaign but has since suggested that he would target less than that.

More than 60 donors gathered at Trump Tower and a nearby restaurant to hear a presentation from Trump. One prospective donor, John Catsimatidis, a grocery store magnate and former New York mayoral candidate, said Trump stressed his love for the country.

Catsimatidis added that the meeting did not set any specific fundraising goals or provide guidance for which Super PAC to fund.

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2:18 p.m.

President Barack Obama is announcing his formal endorsement of Hillary Clinton.

In an online video, Obama calls on Democrats to unify behind his former secretary of state's bid and "build on the progress" of his eight years in the White House.

"I want you to be the first to know that I'm with her," he says.

Obama is also praising Democratic primary candidate Bernie Sanders for engaging young voters and highlighting the issues of income inequality and money in politics. "Embracing that message is going to help us win in November," says Obama.

Clinton and Obama will campaign together in Green Bay, Wisconsin, on June 15.

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1:50 p.m.

A spokesman for Bernie Sanders says the Vermont senator had a "wide-ranging discussion" with President Barack Obama about issues facing working families and ways to "create an economy that works for all people," not just the wealthy.

Sanders spokesman Michael Briggs says that Sanders requested the meeting with Obama because he was "interested in his input." Briggs says Sanders considers Obama to be "one of the smartest people he knows" and was happy to receive his counsel during the hourlong meeting.

Sanders was meeting later Thursday with Senate Democratic leader Harry Reid of Nevada and Charles Schumer of New York, the No. 3 Democrat in the Senate. Sanders was also meeting with Vice President Joe Biden at the Naval Observatory later in the day.

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1:16 p.m.

Vermont Sen. Bernie Sanders says he has a long list of issues he plans to pursue when the Democratic Party holds its nominating convention in Philadelphia at the end of July.

After meeting with President Barack Obama, Sanders tells reporters that the U.S. is the wealthiest nation in the world and should not have millions of senior citizens and disabled veterans struggling to put food on the table because of inadequate Social Security benefits.

He says the U.S. should not have Americans living in some of its inner-cities and rural areas with life expectancies lower than third world countries.

He also is bemoaning the debt facing college students, crumbling infrastructure and the influence that billionaires have on politics, the economy and the media.

Sanders is promising to continue his run at least through next week's primary in the District of Columbia.

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1:10 p.m.

Presumptive Republican presidential nominee Donald Trump is gathering potential donors and party leaders for a meeting in New York City.

Republican National Committee Chairman Reince Priebus and New Jersey Governor Chris Christie, a Trump supporter, are among those in attendance Thursday. Meetings are being held at Trump Tower and a lunch is underway at The Four Seasons in Manhattan.

Woody Johnson, former Jeb Bush backer and owner of the New York Jets, was among the potential donors spotted going into the lunch.

Trump waved and the waiting press but did not comment. He stayed for about 30 minutes. His fundraising operation is off to a slow start and badly trails his likely general election opponent, Democrat Hillary Clinton.

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12:47 p.m.

After wrapping up his meeting at the White House, Vermont Sen. Bernie Sanders says he looks forward to meeting with Hillary Clinton in the future to see how they can work together to defeat Donald Trump in November's election.

Sanders spoke to reporters after meeting with President Barack Obama in the Oval Office.

Sanders did not endorse Clinton. He says he plans to remain in the race through next week's primary in the District of Columbia, and will focus on the need for statehood for the district.

Sanders also said he will do everything in his power to make sure Trump does not become the next president of the United States

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11:58 a.m.

Senate Minority Leader Harry Reid has congratulated Democratic presidential nominee Hillary Clinton on becoming the presumed Democratic presidential nominee.

That's the word Thursday from the Democrat's office. Reid had endorsed Clinton several weeks ago. The senator was meeting with Clinton's rival, Vermont Sen. Bernie Sanders, on Thursday as Democrats press for unity after a hard-fought primary campaign.

Party leaders recognize that the process won't be easy. The top Democrat in the House, Nancy Pelosi, acknowledged that on Thursday.

"People have their hopes and dreams, their aspirations riding on a candidate. And sometimes it's really harder for the supporters to come to reconciliation than it is the candidate," Pelosi told reporters. "Bernie Sanders knows what's at stake in this election, what's on the line. I have no doubt that he'll be very constructive as we go forward."

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11:38 a.m.

President Barack Obama and Bernie Sanders are meeting in the Oval Office.

Obama greeted Sanders as he arrived at the White House and the two walked past the sun-bathed Rose Garden — and a pack of snapping cameras — to their private meeting.

The president and Sanders could be seen chatting warmly and laughing as they strolled along the colonnade. Obama was expected to talk about ways Sanders can keep up the fight for his policy agenda, but not his bid for the presidency.

All the scrutiny around the meeting with the president didn't appear to faze the Vermont senator. Ever the everyman, Sanders stopped for coffee and a scone at a Peet's coffee shop across from the White House before arriving.

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11:25 a.m.

Senate Democrats are unveiling a reform agenda that proposes new curbs on campaign finance spending and a permanent ban on lobbying by former members of Congress.

The "We the People Act" also would prohibit financial services companies from paying bonuses to executives who leave the private sector to take high-level jobs in the government.

The agenda touches on some of the issues and themes that Sen. Bernie Sanders has talked about in his presidential campaign. Democrats led by Sen. Chuck Schumer of New York were unveiling it on the same day that Sanders is visiting the White House and Capitol Hill for meetings with President Barack Obama and Senate Minority Leader Harry Reid.

Senators now have a two-year ban on lobbying after leaving office, and House members a one-year ban.

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11:10 a.m.

Bernie Sanders has arrived at the White House to discuss the future of his presidential bid with President Barack Obama.

Sanders and Obama are due to talk privately in the Oval Office. Sanders' wife, Jane, accompanied him.

The White House says the Vermont senator requested the meeting. Obama plans to talk about ways Sanders can keep up the fight for his policy agenda, but not his bid for the presidency.

Obama is expected to formally endorse Hillary Clinton shortly after the meeting.

Obama's endorsement will add to a growing chorus of Democratic leaders pushing Sanders to step aside so the party can focus on taking on Republican Donald Trump.

The president last spoke with Sanders Tuesday night, shortly after Clinton declared victory in the long primary.

The men are not known to have much of a personal relationship. But the White House says they've spoken more frequently in recent weeks. The White House says this will be their fourth conversation in the last month.

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10:12 a.m.

Democratic presidential candidate Bernie Sanders has landed outside Washington for meetings with President Barack Obama at the White House and with Senate Democratic leader Harry Reid on Capitol Hill.

Sanders faces questions about whether he will back Clinton and when he may end his bid. He lost four of six contests in Tuesday's primaries and Hillary Clinton is now the Democrats' presumptive nominee.

But Sanders has vowed to campaign through Tuesday's final primary in the District of Columbia and pursue a contested Democratic convention in Philadelphia.

Sanders was headlining a D.C. rally and then returning home to Vermont on Thursday night.

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3:13 a.m.

On the verge of endorsing Hillary Clinton, President Barack Obama will pay tribute to Bernie Sanders' historic candidacy for presidency with an Oval Office meeting. The session is aimed at unifying the Democratic Party for a general election brawl with Donald Trump.

Sanders heads to the White House under intense pressure to drop out and clear the way for Clinton. Though he showed signs he understood the end was near, he's vowed to keep fighting for his movement.

Obama has sought to give the Vermont senator the courtesy of exiting the race on his own terms, but is expected to formally endorse Clinton after the meeting. The White House says he plans to use the meeting to discuss how to build on the enthusiasm Sanders brought to the primary.

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This story has been corrected to reflect that Schumer is the No. 3 Democrat in the Senate.

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Corrects length of Obama's tenure to eight years.