Democratic presidential candidate Bernie Sanders speaks during the Iowa Democratic Party's Jefferson-Jackson Dinner in Des Moines on Saturday. (Charlie Neibergall/AP)
Chief correspondent

— Sen. Bernie Sanders has long said that he would not run a negative campaign against Hillary Rodham Clinton. But his campaign took on a decidedly sharper edge Saturday night at the Iowa Democratic Party’s Jefferson-Jackson Dinner.

Sanders (I-Vt.) never mentioned the former secretary of state and current front-runner for the Democratic presidential nomination by name, but his message was clear: He has been a man of conviction, prepared to upend the system; she is too often a political weather vane, too cautious and catering to the political establishment.

Sanders used his speech to draw the sharpest contrast with Clinton of his campaign. On the issues he chose to highlight, Sanders said he had taken positions that challenged the establishment and were politically unpopular at the time. He suggested that Clinton came around only when the politics were more favorable and as the Democratic Party moved to the left.

What issues did Sanders highlight?

The Iraq war, for starters. He opposed the use-of-force resolution when it came up for a vote in Congress in 2002. Clinton did not. It took years for her to express regret and say that she made a mistake.

On trade, Sanders said he never called the Trans-Pacific Partnership trade pact the “gold standard,” as Clinton did when she was secretary of state. He noted that he has opposed it from the start, along with other trade agreements. She now opposes the pact as ultimately negotiated.

Sanders said that he was always against the Keystone XL oil pipeline and that it wasn’t a particularly tough call. Clinton only recently took a position on it — also in opposition.

He said he supported gay rights when it was not easy to do so and implied that her record is mixed.

Both now rail against big money in politics and the power of super PACs, but she has a super PAC helping her candidacy. He said he doesn’t and never will.

Sanders drew enthusiastic support from his supporters, who filled one side of the arena Saturday, but in launching this criticism of Clinton, he faces a pair of challenges. One is obvious: If he and Clinton now agree on many of the issues the senator from Vermont highlighted Saturday, will Democratic voters reward him just because he got there first? The other is how Sanders takes what he said Saturday and turns it into a positive and ­forward-looking message that can expand his base of support.

The reviews of his speech were generally positive Saturday, and his supporters loved it. But some dissent was registered. The sharpest critique said that Sander’s speech was too much about himself and the past, not about the voters and the future. Sanders appeared to be channeling President Obama’s speech at the same dinner in 2007, when the then-senator drew a sharp contrast with Clinton, but Sanders did it without the uplifting and aspirational parts of Obama’s message.

Hillary Clinton and Bernie Sanders and the other candidates took on gun control, Benghazi and other big issues at the first Democratic presidential debate of the 2016 race. Here are the highlights. (Sarah Parnass/The Washington Post)

There was little question that Sanders had the most at stake at Saturday’s dinner. Clinton arrived in Iowa, accompanied by her husband, former president Bill Clinton, and aided by singer Katy Perry, after two of the best weeks of her campaign.

A month ago, Clinton was viewed as a weakened and vulnerable candidate, dogged by questions about her use of a private e-mail server while secretary of state and saddled with voters’ doubts about her honesty. Democrats skeptical about her long-term prospects were encouraging Vice President Biden to challenge her.

But she delivered a strong performance at the Democratic debate in Las Vegas, with a boost from Sanders about her e-mails. She then easily weathered 11 hours of grilling from Republicans on the House Select Committee on Benghazi. She also got a boost when Biden announced that he would not enter the race (although Sanders’s advisers say that decision was equally good for both the candidates).

Some of her problems remain, especially in the context of a general election. But by the time of Saturday’s dinner, Clinton had calmed the nerves of many Democrats and appeared to have regained some of the momentum lost during the summer, with poll numbers rising in some of the early states.

That put the focus on Sanders. He needed to step up and make the next month of the campaign as helpful to him as October has been to Clinton. His speech reflected a turn in his campaign strategy as the candidates began the 100-day countdown to the Iowa caucuses.

Sanders’s campaign manager, Jeff Weaver, played down concerns about the front-runner’s newfound momentum. “Has she had a good couple of weeks? Yeah,” he said as the Iowa activists emptied out of Hy-Vee Hall late Saturday. “They stopped bleeding. That’s what the last two weeks were.”

Senior Sanders adviser Tad Devine attributed Clinton’s improved poll numbers to the millions of dollars her campaign has spent on advertising in Iowa and New Hampshire. He said Sanders’s ads are coming soon, and he predicted they would give the senator a boost.

Devine said the campaign has simply reached the point where Sanders has to draw contrasts that he had not done before. “We need to simplify this race and make it clear to voters that there are real differences between Hillary and Bernie and those differences revolve around issues that are important to the voters,” he said.

Clinton and Sanders weren’t the only candidates on the stage Saturday. The other was former Maryland governor Martin O’Malley. He showed off his oratorical skills and progressive record and used part of his speech to remind the audience that Sanders hasn’t been on the same page as many progressives on gun control, an issue that has gained significant currency for Democrats.

O’Malley’s strong rhetoric has not translated into greater support — something that puzzles many Democrats, who wonder whether it’s because Sanders occupied the territory before O’Malley had a chance to get there. He probably will target Sanders as much as Clinton as the caucuses near and as he attempts to become a factor in the contest.

The Iowa Jefferson-Jackson Dinner is an event that has changed the course of some Democratic presidential campaigns. In the fall of 1999, then-Vice President Al Gore effectively ended former senator Bill Bradley’s challenge in the nomination campaign with his speech at the event. Obama’s 2007 speech gave his campaign a badly needed jolt of energy that eventually resulted in his caucus victory over Clinton, who finished third. Without Iowa, he might not have been elected president.

There was no such clear winner Saturday night, only the hint of things to come. Sanders laid down markers for the next phase of the campaign, foreshadowing a more vigorous debate with Clinton. It was the start of something different, but only a start. Where will he take it next?