With Iowa kicking off the 2016 election season in one week, Democratic presidential front-runner Hillary Clinton tried to erase doubts about her judgment raised by rival Bernie Sanders on Monday while digging deep into her years of governing experience.

At a CNN town hall meeting, Sanders argued that his own judgment, not Clinton's experience, is the most crucial quality for the next commander-in-chief. Clinton, in response, evoked President Barack Obama, saying when he selected her to be secretary of state, he gave approval to her judgment.

"You have to have somebody who is a proven, proven fighter," Clinton said.

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Anxious to put down a threat from the democratic socialist, Clinton faced the challenge of convincing Democratic voters not to be swayed by Sanders' populist rhetoric and to stick with her despite a clamor for candidates outside the political establishment.

The town hall at Drake University lacked the feel of a normal debate. It featured separate appearances by Sanders, former Maryland Governor Martin O'Malley and Clinton and all three took audience questions at the event.

Clinton was more animated than usual, raising her voice to make points, and Sanders made the audience laugh with some jokes. The overall tone was polite, in contrast to a more rancorous fourth debate between the three last week.

Sanders cited Clinton's 2002 Senate vote to authorize the Iraq war and her prior support for the Canada-to-Texas Keystone Pipeline as evidence that her experience is misguided. Clinton has shifted her position on both issues, while Sanders opposed both from the start.

"Experience is important but judgment is also important," he said.

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Sanders also defended his call for raising taxes to fund a "Medicare-for-all" program, U.S. infrastructure and tuition-free college education.

"We will raise taxes. Yes, we will," said Sanders, a Vermont senator. But he said the money would actually save money for families because they would no longer pay health insurance premiums.

Clinton has been making the case that her time as secretary of state and a senator from New York, make her more experienced. But on the town hall stage on Monday, she pushed back at Sanders' judgment argument by evoking Obama, who remains popular with Democratic voters and was critical of her Iraq War vote when the two competed in 2008.

"[Obama] ended up asking me to be secretary of state," Clinton said. "It was because he trusted my judgment and we worked side by side over those four years."

Clinton, who lost the Democratic primary to Obama in 2008, was for months the clear front-runner to be the party's nominee this time around, but opinion polls have showed a surge of support for Sanders in recent weeks.

She argues that while Sanders' goals on issues such as social inequality are laudable, some are unobtainable and he lacks the experience to tackle a wide range of issues.

"When you're in the White House you cannot pick the issues you want to work on, you've got to be ready to take on every issue that comes your way, including those you cannot predict," Clinton told the Jewish Federation of Greater Des Moines on Monday.

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Clinton also went to great lengths at the town hall to criticize Republican front-runner Donald Trump, particularly for insulting minorities. "He started with Mexicans, he's now with Muslims," she said.

Clinton got some much-needed praise from President Obama in a Politico interview published on Monday, exactly a week before Iowans hold the nation's first nominating contest for the Nov. 8 election.

While never explicitly criticizing Sanders, whose campaign is focused on pledges to redress social inequality and contain Wall Street excesses, Obama praised Clinton's experience and suggested several times that Clinton's messages are grounded in realism.

"[S]he’s extraordinarily experienced — and, you know, wicked smart and knows every policy inside and out — [and] sometimes [that] could make her more cautious, and her campaign more prose than poetry," Obama said.