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CHICAGO—On the day after Senator Bernie Sanders lost the Nevada caucuses, he held just one event in Greenville, South Carolina.

During what was then his normal stump speech, he did not mention his primary challenger’s name once. Not even the words, “my opponent.”

Sanders has not gone a single day without criticizing Hillary Clinton since.

The candidate who went out of his way to avoid attacking his rival throughout the summer, fall and winter has relentlessly unleashed on Clinton for three straight weeks, focusing on familiar talking points now strung together as a fixture of his stump speech.

“Now let me say a few words about some of the strong differences of opinion that I have with Secretary Clinton,” he now normally begins one portion of his speeches before hitting her on a litany of issues. The go-to critiques include trade, the Iraq War, and Clinton's use of Super PACs.

Boos and heckles quickly arrive from his supporters as they outwardly delight in hearing the differences between their candidate and the Democratic frontrunner.

"There is something wrong when Secretary Clinton has a Super PAC which is collecting millions of dollars from Wall Street, from the fossil fuel industry, from the drug companies,” proclaimed Sanders at the University of Illinois Urbana-Champaign last week to wild cheers.

“Secretary Clinton voted for [the Iraq] war,” he pointed out to a thrilled crowd in Charlotte, North Carolina. "In my view, the war in Iraq was one of the worst foreign policy blunders in the history of the United States.”

“I proudly stood with the workers! Secretary Clinton stood with the big money interests!” Sanders enunciated in Youngstown, Ohio on Monday when illustrating Clinton’s support for trade deals such as the North American Free Trade Agreement (NAFTA).

While these critiques have popped up occasionally in the Sanders contrast canon for months, they now come as a hallmark of his daily campaign speeches.

Depending on the day, Sanders also has dinged Clinton on her and her husband’s support of the “homophobic” Defense of Marriage Act (DOMA) and her support from former Secretary of State Henry Kissinger.

“I do not want Henry Kissinger to ever praise me!” he roared during a Michigan rally at Grand Valley State University near Grand Rapids.

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The shift in tone has been drastic. In 2015 and early 2016, even uttering Clinton’s name would draw headlines—then unwanted by the candidate himself.

“I cannot walk down the street—Secretary Clinton knows this—without being told how much I have to attack Secretary Clinton,” Sanders told NBC News' Andrea Mitchell during the NBC's January Democratic Debate, “Want to get me on the front page of the paper? I make some vicious attack. I have avoided doing that. I am trying to run an issue-oriented campaign.”

He still emphasizes issues, but things have changed since that debate.

In the 21 days following the Nevada caucuses, Sanders held five official press conferences during which he explicitly criticized Clinton on a variety of issues.

During a Saturday morning press conference in Chicago for example, he spent his time negatively linking Clinton to Mayor Rahm Emanuel and his cutting of funding for public education programs.

Minutes later, Sanders went on to imply that because she utilizes Super PACs, Secretary Clinton did not represent the “future of the Democratic Party.”

On the night of Republican frontrunner Donald Trump’s cancelled Chicago rally that descended into chaos and violence just 12 miles away from a Sanders event, the senator dedicated more time to hitting Clinton than to going after Trump.

NBC News asked Sanders at a press conference why he was highlighting these differences so strongly in recent weeks after relatively holding off for months. The candidate brushed off the question.

“I don’t think that’s accurate,” said Sanders waving his finger saying that he is not engaging in the same kind of “sixth grade food fight” of the Republican race.

"What we are trying to do -- and have from Day One -- is differentiate our differences, which are very strong, with Secretary Clinton,” the Vermont senator explained.

Later in the same response, Sanders went on to say that the "history books" will show that he "was right" and “Secretary Clinton was wrong" on trade.

“He’s never hesitated to talk about those issue areas where they have significant contrasts,” Sanders’ communications director Michael Briggs told NBC News.

“Now, has that gotten a little bit more forcefully stated in some of the rally speeches? I’ll grant you that,” Briggs added. He agreed, however, that it was not as much a reaction to any event, but rather a “natural development” as the race continues on.

The Sanders campaign still insists that there is a big difference between pointed contrasts and “attacks and negative ads,” sometimes pointing to the fact that Clinton’s name nor face has ever appeared in a television spot of theirs.

Though just this past weekend, the campaign released an ad focused on trade in North Carolina. A narrator says in the spot: “While his opponent has flip flopped on trade deals, Bernie has fought them and stood with American workers.”

Either way, one thing is clear: his fans are reveling in his ramped up criticisms.

Jelena Mihajlovic, a 17-year-old high school student from Westmont, Illinois who intends to participate in the state's primary Tuesday as she will be 18 by general election day, said she believes Sanders needs to call Clinton out as often as possible.

“He needs to point out some of her flaws. He’s doing his job because he needs to make sure that we see what we need to see,” she said.

John Cole, an account manager at a startup who drove from Milwaukee to see Sanders in Chicago Monday night, thought drawing the contrasts has been helpful to him as well.

“I think he’s going after her for the right reasons,” Cole told NBC News. “He’s kind of showing that there’s two sides to her, and I’m glad I’m seeing that side I haven’t seen."

Booing and jeering have now become commonplace when Sanders brings up Secretary Clinton’s name at his rallies.

On the second day of Sanders’ multi-week streak of Clinton contrasts, the crowd booed his opponent's name at an event in Norfolk, Virginia. Sanders immediately held his hands up and shook his head.

“No. No. Nope, nope, nope.” said Sanders quieting the room, “I respect Secretary Clinton, we can have differences.” The crowd applauded and the booing abated.

He has not stopped a booing crowd since.