DES MOINES — Bernie Sanders is giving Hillary Clinton a pass on her “damn emails,” but he’s giving her hell on just about everything else.

On Saturday night, at the high-stakes Democratic Jefferson-Jackson dinner, the Vermont senator launched a new, frontal attack on Clinton’s record, caution and character — a direct response to her recent surge in the polls here and nationally, and fueled by her strong performance at the first Democratic debate earlier this month. The shift represents a gamble: Can a nice-guy candidate publicly dedicated to running on substance turn to attack mode without sacrificing his reputation as an authentic voice of the people?

The skirmish began even before each campaign's supporters — hundreds of them, each with their own signs, noisemakers and pre-rehearsed chants — began filing into a drafty hall at the Hy-Vee Center in downtown Des Moines, where the annual kingmaker’s ball takes place. At a pre-dinner rally, Sanders’ supporters flew a single-engine plane with the banner “FEEL THE BERN” directly over a Clinton rally headlined by the pop singer Katy Perry. During Clinton’s introduction at the dinner, Sanders' supporters — many of them in their teens and twenties — tried to drown out her intro with cheers for the democratic socialist. And they filed out quietly when she took the stage to speak, a hint of how passionately they feel about Sanders and their ambivalence about Clinton.

The Vermont senator, as always, did not go after the front-runner in a personal way or mention her by name. Instead, he delivered a fiery yet indirect indictment of her entire political career. In his 25-minute speech — backed up by the thundering chants of supporters chanting “Feel the Bern!” — he attacked Clinton’s slowness to take a position on the Keystone pipeline: “This was not a complicated issue,” he said. He lambasted her for now opposing the Trans-Pacific Partnership, which she once called the “gold standard” of trade deals.

“It is not now, nor has it ever been, the gold standard of trade agreements,” Sanders said. And he reached back to Clinton’s 2002 vote to support the war in Iraq, an issue that plagued her eight years ago when she took the stage here. “When I came to that fork in the road I took the right road, even though it was not the popular road at the time,” he said.

Clinton, fresh off her steady, disciplined performance before the House Benghazi committee, doesn’t tend to shine in big set-piece, theater-in-the-round speeches, and Saturday was no exception. Compared with the passionate populist broadsides delivered by Sanders and former Maryland Gov. Martin O’Malley, Clinton was more measured — except for the moments when she spoke about the struggles of Iowans she’s met while campaigning or her role as a gender pioneer.

“Sometimes when a woman speaks out people think it’s shouting,” she intoned — a reference to Sanders’ accusation that she was “shouting” about gun control during the debate.

But the most pointed remarks were aimed by a plateauing Sanders at an ascendant Clinton. Nor was she the only Clinton he targeted. As Bill Clinton raises his profile, Sanders is increasingly criticizing him for his trade policy and social issues stances from the 1990s. Target No. 1 Saturday night: Clinton’s support of the anti-gay marriage Defense of Marriage Act. “In 1996, I faced another fork in the road — another very difficult political decision,” Sanders intoned. “It was called the Defense of Marriage Act, brought forth by a Republican-led Congress. Its purpose was to write discrimination against gays and lesbians into law.

“Let us remember, that support for gay rights back in 1996 was not what it is today,” he added — a pointed reminder of the Clintons' recent-vintage support of gay marriage.

He presented himself as the stalwart contrast. “I did not support it yesterday,” he said of the Trans-Pacific Partnership. “I do not support it today. And I will not support it tomorrow.”

For most of the campaign, Sanders has ridden in the slipstream behind Clinton, capitalizing on her errors while solidifying his own support among educated whites on the party’s left wing. But a revitalized Clinton — and the absence of a Joe Biden candidacy to redefine the race in his favor — now necessitates a mid-course correction. And on Saturday night, Sanders campaigned like a man with something to lose.

He sought to seize the outsider mantle that helped elect President Obama eight years ago, beginning in the same room. 

“I promise you tonight as your president I will govern based on principle not poll numbers,” he said, echoing the 2007 speech here by Obama, who also drew a distinction with Clinton and said he would govern “not by polls, but by principle.”

Sanders has recently implied he will not campaign on Obama’s record. But he bear-hugged him Saturday night. “Eight years ago the experts talked about how another Democratic candidate for president, Barack Obama, couldn’t win,” he said. “How he was unelectable. Well, Iowa, I think we’re going to prove the pundits wrong again. I believe we will make history.”

Clinton arrived in Iowa Saturday afternoon eager to deliver a winning performance at the event that launched Obama’s campaign into the stratosphere — and the sting of that pivotal event appeared to be at the forefront of the campaign’s planning.

“We are geared up and ready to go!” Clinton said at the pre-dinner parking lot rally with Katy Perry. That phrase echoed Obama’s “Fired up! Ready to go!” call- and-response chant that tore through the room — and shocked a less organized, less fired-up Clinton campaign that was based on experience and competence. 

Bill and Hillary also were among the last people to leave the arena — they lingered on the rope line, signing books and taking selfies for close to an hour after event ended and all the other candidates had departed.

Hours before the dinner, the Clinton campaign announced an endorsement from David Plouffe, Obama’s 2008 campaign manager. “To be honest, during the most intense days of the 2008 primary, I would never have imagined writing this,” said Plouffe. “And I doubt Team Clinton felt any differently about me. … She’s the right person to protect President Obama’s legacy on health care and so much else.”