CHICAGO (AP) — Chicago Mayor Rahm Emanuel doesn't face any big-name challengers in his push for a second term, but the former White House chief of staff isn't taking any chances.

He's pulled in more than nine times more money than any of his challengers through fundraising and a PAC. He's dominated the airwaves with commercials, including a radio spot this week featuring an endorsement from his old boss, President Barack Obama. And he's agreed to attend no less than six forums and debates — far more than the single debate he did during his 2011 bid to lead the nation's third-largest city.

Never known to be bashful, Emanuel says he takes every challenge seriously. But his unwillingness to coast to re-election is rooted in political reality.

He has struggled with poor popularity ratings after confronting contentious issues like school closures and gun violence that resonate in Chicago's neighborhoods. And he appears determined to capture a majority in the Feb. 24 vote to avoid an embarrassing April runoff that could allow a sole remaining challenger to consolidate the opposition.

Since launching his bid, Emanuel has defended his policies by taking a set of campaign talks on the road and confronting his challengers head-on, a change from his first campaign when he largely stayed out of the fray. He's asked his opponents to release tax returns and turned the intensity up this week, going after two candidates in the first debate.

"If you look at it, there's only one candidate that is drawing strength from the entire city of Chicago, not just parts of it," Emanuel told reporters Thursday after receiving an endorsement from trade unions.

The contest features an outspoken alderman, a county commissioner, an activist and a millionaire businessman, the only other candidate with enough money for television ads.

Emanuel has more than $16 million to help him, most from his own campaign fund. The money includes donations from labor, business executives and Hollywood.

The challengers say they're not intimidated.

"It's easy to see he's vulnerable by the amount he's raising that is absolutely obscene by any standard," said two-term Alderman Bob Fioretti, a frequent voice of dissent on a City Council that often backs the mayor's ideas.

Emerging as another potential top challenger is Cook County Commissioner Jesus Garcia, a former alderman and state lawmaker who has support from the city teachers' union. He's billing himself as the neighborhood candidate, often stressing his decades living in Chicago and raising a family.

The others are political newcomer Willie Wilson, who boasts of building a successful medical-supply company despite receiving only a middle-school education. He's put more than $1 million of his own money into the race. Perennial candidate William Walls, an activist, is also running.

They've capitalized on the schools issue.

Emanuel's relationship with schools has been especially strained after tense contract negotiations led to a teacher's strike in 2012. The following year, he pushed to close dozens of schools to cut costs, despite angry protests. Advocacy groups have continued to question the cost savings and are demanding an elected school board instead of one appointed by the mayor.

The public-school turmoil pitted Emanuel against Chicago Teachers Union President Karen Lewis. A frequent and vocal critic of Emanuel, she was seen as his fiercest challenger until she dropped her potential bid because of serious illness. She now backs Garcia.

The challengers are hoping to get enough votes to force an April 7 runoff, which would happen if Emanuel isn't able to capture 50 percent plus 1 vote.

A Chicago Tribune poll released Thursday showed Emanuel with 42 percent, Garcia 18 percent, Fioretti 10 percent, Wilson 7 percent and Walls 2 percent. The poll, conducted Jan. 22 through Tuesday, drew on telephone interviews with more than 700 registered voters. It had an error margin of 3.7 percentage points.

Emanuel won the mayor's race with 55 percent of the vote in 2011, when former Mayor Richard Daley retired after 22 years in office.

On the campaign trail, Emanuel has focused on improvements, like working with environmental activists and hiring minority contractors to upgrade a portion of the city's Red Line train tracks. When launching his re-election bid in December, Emanuel told supporters a vote for him would continue progress for a "new Chicago."

But his rivals challenge the notion that he represents all Chicagoans.

"The neighborhoods," Garcia said, "appear to be an afterthought and stand in contrast to the vitality and wealth in the central business district."

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Follow Sophia Tareen at http://twitter.com/sophiatareen .