CHICAGO — When Bernie Sanders launched his long-shot bid for the presidency 10 months ago, there were two words that rarely crossed his lips: Hillary Clinton.

Now he can’t seem to stop talking about her – and not much of what he has to say is very nice.

During a boisterous rally here, the senator from Vermont dinged Clinton for supporting a series of “disastrous” trade deals. He mocked her for refusing to release transcripts of paid speeches she gave to Wall Street firms. He said she was wrong to vote for the Iraq War in 2002.

The transformation has been stark. What’s less clear is whether Sanders’s rhetoric helps explain his lasting power in a nominating contest that appears likely to drag on for weeks, considering the mounting number of victories he has scored in key states.

So far, the evidence is mixed. In Michigan last week, Sanders won a surprising though narrow victory after closing a gap of more than 20 percentage points in the polls. He was relentless in the days before the election in criticizing Clinton on trade. But Sanders also got trounced the same day in Mississippi – albeit a state where he didn’t mount much of a campaign.

Tuesday – a day when five states hold primaries – should give a better indication of whether Sander’s tough talk is paying off.

One of those contests is in Illinois, and Sanders isn’t holding back as he campaigns here. In Chicago on Friday, Sanders even took aim at Clinton for her close association with Mayor Rahm Emanuel, whose approval ratings are in the tank, particularly among black Chicagoans.

“I want to thank Rahm Emanuel for not endorsing me. I don’t want his endorsement!” Sanders screamed, to the delight of a crowd estimated at 9,000 people. “I don’t want the endorsement of a mayor who is shutting down school after school and firing teachers.”

To drive home his point, Sanders held a news conference the next day devoted entirely to Emanuel. He told reporters that if he were Clinton, he would have refused the mayor’s support.

Compared with the Republican presidential race and other elections in past years, the Democratic contest remains relatively tame. But the Bernie Sanders who is fighting to remain relevant in the delegate chase against Clinton sounds quite different from the Sanders whose chief antagonist was the “billionaire class” when he debuted on the campaign trail last spring.

Analysts say Sanders’ decision to attack Clinton more aggressively is understandable: It’s what candidates who are behind tend to do. But in Sanders’ case, he risks damaging his brand as an anti-establishment politician who has pledged to stay positive in his bid for the Democratic nomination.

In an interview, Sanders acknowledged that he’s adopted a tougher tone but said he has tried to stick to the issues and not engage in character attacks. To the extent that the race has turned more negative, Sanders said, Clinton is to blame.

“We’re responding,” Sanders said. “I find it disappointing when the secretary mischaracterizes my record.”

Sanders was particularly galled, he said, by Clinton’s assertion during their recent debate in Flint, Michigan, that he had opposed releasing funds to bail out the automobile industry.

Most fact checkers who looked into Clinton’s statement concluded she wasn’t telling the whole story.

In 2008, Sanders voted for an unsuccessful stand-alone bill to provide aid to the auto industry. The bill Clinton referenced came later, and its primary purpose was to bail out Wall Street, something Sanders staunchly opposed. Some money authorized in the bill wound up flowing to major U.S. automakers, though.

“To say that Bernie Sanders, who has perhaps the strongest pro-worker voting record in the United States Congress, does not support automobile workers in their time of need … is totally absurd,” Sanders said. “It’s unfortunate that she made that statement.”

Sanders and his aides have tried to argue that none of his TV ads mention Clinton by name. But some leave little to the imagination.

On Friday, Sanders debuted a pair of ads in Illinois and North Carolina, another state that votes Tuesday, that say that “while his opponent has flip-flopped on trade deals, Bernie has fought them and stood with American workers.”

Clinton’s positions on some trade deals, including the pending Trans-Pacific Partnership, have, in fact, evolved. As secretary of state, she called the TPP “the gold standard” of trade deals. Last fall, she announced her opposition, which she stated even more strongly over the weekend. She has said she now has a fuller picture of what’s being proposed.

In the interview, Sanders said voters have a right to know where he and his opponent diverge.

“The differences are becoming fairly clear to the American people, and the more the differences between her views and my views get out there, the better we’ll be,” he said.

Clinton doesn’t see it that way. During an appearance Saturday in St. Louis, she said Sanders “has decided to close this election by attacking me and misrepresenting my record and his.”

Clinton spokesman Jesse Ferguson said his campaign thinks Sanders has “broken his word” about running a positive campaign.

During a rally Saturday in Springfield, Missouri, Sanders continued to hammer Clinton on trade, saying their views diverged on the North American Free Trade Agreement, which was approved when her husband was in the White House in the 1990s.

“I understood at the end of about three seconds that what this trade deal was about was forcing American workers to compete against very, very poor people in Mexico,” Sanders told his audience.

“I have voted against every one of these disastrous trade agreements,” he said. “Secretary Clinton’s position has been different. She has supported virtually every one of these trade agreements.”

Boos filled the arena at the mention of Clinton’s position.

Sanders has also raised questions about Clinton’s judgment, zeroing in on her decision to deliver a series of paid speeches to corporate interests in the run-up to her presidential bid. That included some addresses to the Wall Street firm Goldman Sachs, which paid her $225,000 for one speech.

On that subject, Sanders hasn’t hesitated to take a snide tone.

“The way I see it, if you’re going to give a speech and get $225,000, it must be a really brilliant speech,” Sanders told a crowd at the University of Illinois on Saturday. “It must be opening new vistas of human thought.”

He also knocked Clinton for refusing to release transcripts of those speeches to the public. She has said she would do so when other candidates are held to the same standard.

“Let me make a dramatic announcement to all of you here today,” Sanders sarcastically told his crowd. Saying he was ready to release transcripts of his Wall Street speeches, he swung open his arms to revel nothing. “Here they are!” he said.

The danger for Sanders, Elleithee said, is not that he will lose die-hard supporters with his tougher tone but that it could be harder to attract new ones – including some who like Clinton and are still weighing whether to vote for her.

Some Sanders fans, including Samuel Nebinger, who turned out Saturday night to see the candidate in Springfield, say they’re not bothered by the more pointed rhetoric. Nebinger said he welcomes it.

Nebinger, 21, recently dropped out of Missouri State University, he said, because it was too expensive, and he now works at a local call center. He was wearing a shirt that said “Help Us, Bernie, You’re Our Only Hope.”

“He wanted to run it clean at first,” Nebinger said. “But he needed to go on the offensive, because she’s been doing so many corrupt things. She did that to herself.”