LAS VEGAS (AP) — Hillary Rodham Clinton entered Tuesday night's first Democratic debate a weakened front-runner, anxious to move past the controversy over her email practices and persuade voters she's the best-qualified candidate to lead the party to a third straight term in the White House.

Clinton, the former secretary of state, faces her biggest challenge from Bernie Sanders, the rumpled independent senator from Vermont who has energized liberals with his call for a "political revolution." Much of the focus in the prime-time contest was sure to be on how they engage each other, given that they have gone long stretches in the campaign without even mentioning each other's names.

Joining them on stage in Las Vegas was a trio of low-polling candidates looking for a breakthrough moment: former Maryland Gov. Martin O'Malley; Jim Webb, a former Navy secretary and U.S. senator from Virginia, and Lincoln Chafee, the Republican-turned independent-turned Democrat from Rhode Island.

While Clinton maintains financial and organizational advantages over her Democratic rivals, months of Republican criticism of her use of personal email and a private Internet server while in the Obama administration have shadowed her campaign and hurt her standing with voters. The Associated Press reported Tuesday that Clinton's server was connected to the Internet in ways that left it somewhat vulnerable to hackers.

The candidates and their teams focused elsewhere for the Democrats' first big TV event.

Maria Cardona, a Democratic strategist who worked for Clinton's failed 2008 White House campaign, said that as long as the email issue didn't dominate the debate, "this will be a win for her no matter how you look at it."

Sanders, too, seemed eager to keep the debate focused on policy, and he was looking to broaden his appeal to more Democratic voters. The self-described democratic socialist, who is drawing massive crowds and challenging Clinton's fundraising prowess, has called for breaking up big Wall Street banks, expanding Social Security and providing free tuition to public colleges and universities.

In recent days, Sanders has stepped up his efforts to draw a contrast with Clinton, casting her as a late-comer to the liberal positions he's held for decades.

After Clinton announced her opposition to a sweeping Pacific Rim trade deal, a pact she had previously called the "gold standard," Sanders said he was glad she'd come around to "a conclusion I reached on day one."

Indeed, Clinton has increasingly moved to the left on domestic policy since announcing her campaign this spring, including voicing opposition to the Keystone XL oil pipeline and support for expanded gun control legislation. While she rarely mentions Sanders by name, she's suggested her proposals are more realistic and well-formed than those espoused by the Vermont senator.

In an interview with NBC's "Today" show last week, Clinton went after Sanders' call for free college tuition, a popular initiative among progressives.

"I'm a little different from those who say 'free college for everybody,'" Clinton said. "I am not in favor of making college free for Donald Trump's kids."

Not on the scene in Las Vegas but on many minds was Vice President Joe Biden.

Biden, flirting for weeks with a late entry into the race, had nothing new to say. His office said he would be watching from his residence in Washington.

Despite the Biden speculation, the Democratic primary has lacked the drama of the Republican contest and the unexpected rise of Donald Trump. Debate host CNN said it expected significantly lower ratings for Tuesday night's debate than for the Republican contest the cable channel hosted in late September, which drew an audience of 23 million.

White House spokesman Josh Earnest said he expected President Barack Obama to watch at least some of his party's debate.

"I don't think that he will watch it wire to wire — there is some pretty good playoff baseball on tonight," said Earnest, referring to the Major League Baseball playoffs.

Even with smaller viewership than the GOP debates, Tuesday's event was sure to be largest audience for Democratic candidates since the primary race began. It's one of six debates the Democratic National Committee has sanctioned, a point of contention among some candidates seeking more nationally televised events to generate attention.

O'Malley, who had expected to be Clinton's chief rival, has led the push for more debates. He's also been sharply critical of what he sees as Clinton's flip-flopping on policy and has said questions about her email use are legitimate.

Webb has been a chief critic of Clinton's early support of the Iraq war and could push her on her hawkish foreign policy positions. It's unclear what role Chafee might play in the debate, given that his most notable campaign moment thus far has been his call for the U.S. to adopt the metric system.

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Pace reported from Washington.

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