DES MOINES — (CNN) Hillary Clinton and Bernie Sanders on Monday drew their sharpest contrasts yet in hard-hitting final pitches to Iowa voters as the competitive race to win the first in the nation caucuses enters its last week.

The Democratic race has often paled in comparison to the rollicking Republican battle. But there was palpable energy at CNN’s town hall as the candidates delivered urgent, passionate pleas for supporters to caucus on February 1.

Sanders offered a vigorous performance punctuated by calls for a progressive revolution. Clinton matched him for energy by arguing that only she had been on the front lines of progressive change for decades and uniquely had the multi-tasking skills at home and abroad needed of a President.

“It’s hard,” she said. “If it were easy, hey, there wouldn’t be any contest. But it’s not easy. There are very different visions, different values, different forces at work, and you have to have somebody who is a proven fighter — somebody who has taken them on and won, and kept going, and will do that as President.”

Sanders, going first before an intimate audience of Iowa Democratic voters, looked more at ease than ever in mounting full-frontal attacks on his rival. He hit Clinton hard over her vote for the war in Iraq, her slow pivot toward Democrats who oppose the Keystone Pipeline and a vast Pacific trade pact. In short, he sought to make the case that she might have the most experience but he had the best judgment.

Clinton, meanwhile, seemed better prepared than she has been for much of her campaign to parry Sanders’ claims that she is a late comer to the cause of economic inequality, and seized on warm words from President Barack Obama in an interview with Politico released Monday to argue that only she could be trusted to win an election and safeguard his legacy.

And there were odd moments of surprise insight into the candidates’ personalities and senses of humor as Sanders related his youthful athletic prowess as a talented elementary school basketball player and Clinton offered a gracious review of Sanders’ widely praised new campaign ad.

Sanders made the vast gap between the rich and poor and the “recklessness” and “greed” of Wall Street the centerpiece of his performance, as he warned that the wealthy would have to pay more in taxes.

“We need a political revolution,” he said. “We are touching a nerve with the American people who understand that establishment politics is just not good enough.”

Sanders dismissed Clinton’s political record, seeking to prove he was closer to the Democratic Party base and just as prepared to be President as Clinton.

“I voted against the war in Iraq … Hillary Clinton voted for the war in Iraq,” Sanders said. “I led the effort against Wall Street deregulation. See where Hillary Clinton was on this issue.”

“On day one, I said the Keystone Pipeline was a dumb idea. Why did it take Hillary Clinton a long time before she came into opposition to the Keystone Pipeline? I didn’t have to think hard about opposing the Trans Pacific Partnership. It took Hillary Clinton a long time to come on board on that.”

He also warned unapologetically that taxes would go up if he is elected President, especially to pay for his Medicare-for-all health care plan.

“We will raise taxes. Yes we will,” Sanders said, but added that American families would be better off overall as they would save money on private premiums.

Eight years after she lost Iowa to Obama, Clinton again faces the unappetizing prospect of losing the caucuses to a candidate who has energized young voters and is coming at her from her left.

But she responded by making her most effective counter yet to Sanders’ charge that she is out of step with the infectious desire for political change that animates her party, particularly among younger voters.

After one young man asked her why voters did not trust her, she said that the only reason she is controversial is because she is a substantive political figure who never gave up.

“They throw all this stuff at me, and I’m still standing,” Clinton said.

Then, warming to her theme, she sought to debunk the idea that her long history as a figure of the political establishment eroded her progressive credentials.

“I have been on the front lines of change and progress since I was your age,” Clinton told the man in one of her most animated moments of the campaign. “I have taken on the status quo time and time again.”

Clinton also said she was “really touched and gratified” by Obama’s warm assessment of her character during the Politico interview, and related how her relationship with her former political rival developed into a close friendship when she served as his first-term secretary of state. She also took a shot at Republican front-runner Donald Trump, rebuking him for targeting Muslims in America and around the world.

And showing a softer side, she praised a Sanders’ ad featuring an evocative tableau of U.S life set against the soundtrack of Simon and Garfunkel’s 1960s folk anthem “America.”

“That’s fabulous, I loved it,” Clinton said, but then quickly pivoted to the crux of her argument: “I believe I’m the better person to be the Democratic nominee and to be the President of this country.”

Clinton mounted a staunch defense of her record as secretary of state, telling Democrats worried about her hawkish instincts that military force should only be used as a last resort. She also claimed credit for framing a sanctions regime on Iran that led to a recently concluded nuclear deal and highlighted an Israel-Hamas ceasefire in Gaza she brokered in 2012.

But Clinton was thrown on the defensive at one point, when she was asked about the controversy over her private email server that has dogged her campaign and is under investigation by the F.B.I. amid claims she recklessly left classified intelligence at risk of being intercepted by foreign spy agencies.

“I’m not willing to say it was an error in judgment because nothing I did was wrong,” Clinton said.

Long-shot candidate Martin O’Malley, the former governor of Maryland, also appeared on stage and argued that he represented a generational change in politics that neither Sanders nor Clinton could match.

“Lift up a new leader, because you can change the course of this presidential race. You can shift this dynamic on caucus night. I know you can, I’ve seen you do it before,” O’Malley beseeched the audience at the end of his pitch.

The latest polls show Clinton and Sanders locked in a tight contest in Iowa. In the most recent CNN Poll of Polls, Sanders edges Clinton 46% to 44% in Iowa, with O’Malley at 4%.

And in a new CNN/ORC national poll published on Monday, Clinton led Sanders 52% to 38% with O’Malley way back at 2%. Though the survey showed a significant cushion for Clinton, her advantage was smaller than at any time since September. The poll showed women, non-whites, self-identified Democrats, and those over age 50 breaking sharply for Clinton. Men, white voters, independents who lean Democratic and younger voters are more likely to support Sanders.

The Iowa contest is particularly important to Clinton, who lost the state in 2008, setting in motion Obama’s path to the White House. A victory for Sanders could reshape the entire Democratic race while a Clinton win could quell jitters in her camp and help put her on the path to the nomination.

Clinton, however, insisted she wasn’t worried.

“I’m proud of the campaign we’ve run and what we’ve put out there before the American people,” she said. “It’s a tough campaign and it should be because it’s the toughest job in the world.”

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