No more Mister Nice Guy for Bernie Sanders. The relatively genteel campaign that built his brand is giving way to more aggressive, personal attacks on Hillary Clinton.

The sharp turn in the Democratic race occurred the morning after Sanders’s strong win in Wisconsin, with reports that the Clinton campaign would intensify efforts to “disqualify” Sanders.

“We saw that strategy immediately,” says Sanders strategist Tad Devine, recalling how Clinton wouldn’t answer the question, “Is he qualified?”

“It was a simple question, and if it was just her and that one question, that would be one thing,” says Devine. But then her surrogates piled on, questioning whether Sanders is up to the job, with Clinton campaign overlord John Podesta conceding only that Sanders would be “much better than Donald Trump.”

Devine was on Hardball and shot back, “My 28-year-old daughter would be much better than Donald Trump. At least she interned at the White House and has some experience.”

Devine told The Daily Beast in a phone conversation that “we had to go back at them [the Clinton campaign],” and New York is the place. “The political culture of America is very different,” he said. In Iowa, if you push back hard, “you’re not going to be around long. But if you go to New York and you have someone who is tough and aggressive and someone who’s not going to engage, the tough and aggressive candidate wins.

“We’re determined not to be the victim,” he said.

Clinton’s refusal to say Sanders is “qualified” set the stage for the cage match along with festering grievances about Clinton portraying Sanders as a tool of the gun lobby, aggravated by what Devine calls her “specious” case about Vermont guns feeding violence in NY. (The Washington Post gave it three Pinocchios.) Sanders is hitting fracking hard upstate, calling for a federal ban, and tying it along with the Wall Street money Clinton has received to the theme, “You can’t make the right political decisions unless you are free of the influence of special interests,” Devine said.

Devine dismissed the notion that Sanders’s attacks could hurt Clinton in the general election. “I don’t think anything we’ve said is going to be effectively used by the Republicans.” Sanders has said repeatedly he will support the nominee, and once the primary battle is resolved, Devine says there will be unity “because the alternative is unacceptable.”

He’d like Sanders to get some credit for not talking about Clinton’s most conspicuous vulnerabilities, the email investigation and Clinton Foundation conflicts of interest. But those are not topics that move Democratic primary voters. There will be plenty of ground left for the GOP to plow.

A year ago this past weekend, Devine was in Vermont talking to Bernie and Jane Sanders about the race—they had no campaign, no money in the bank for a campaign, and no organization. When he headed back to the airport, he wasn’t sure what they would do. “I’m proud of how far we’ve come,” he says, which is farther than anyone could have imagined, including Sanders, the truest of the true believers.

“When you get into this and you have a chance to win, you want to win,” says Devine.

If you were a reporter and you called Devine before the Wisconsin primary, he predicted Sanders would win. He’s not predicting a win in New York, where the polls show Clinton with a strong lead—“and the only way we get superdelegates in large numbers is with big convincing wins that make them see he’s a much stronger candidate than she is,” he says.

“If we have a winning strategy, it’s a huge win in California, then we get to the point where the superdelegates take a look, and we make our case.”

What if those victories don’t materialize? Devine wouldn’t address what’s next for Sanders. “We haven’t gone into past-campaign mode. We’re still in planning-to-win mode,” he said. But he did agree that win or lose, Sanders is not going away.

And that’s the crux of the story: Sanders’s staying power and where he takes it. Clinton’s repeated sniping at Sanders (and vice versa) is having its effect. There is booing when he mentions her name at rallies. Sanders used to say “no, no,” now he lets the booing ring out.

There’s still time to mend this, and the burden for now is on Clinton. It’s asymmetrical warfare in the sense that Clinton, in order to win in November, needs Bernie’s people, and he doesn’t need hers. Sanders almost certainly won’t be the nominee, and he can retain his outsider/protest/movement status much better without any reconciliation.

Yes, calling Clinton “unqualified” went over the line, but that’s not what matters. What matters is how Clinton deals with Sanders between now and Election Day. The Revolution that Sanders is calling for may not carry him to the White House, but the legions of people he has inspired will make him a force to be reckoned with once he returns to the Senate and joins with Elizabeth Warren. Together they will be a thorn in Clinton’s side or the core of a powerful Clinton legislative agenda should she become president. The seeds for that future relationship are being sown now.