For months, Bernie Sanders and his supporters have pointed to polls that show him running comfortably ahead of Donald Trump in November. But now that Hillary Clinton’s lead over Trump has disappeared — and the two likely nominees are now running neck-and-neck in national polls — his argument is gaining new resonance.

Clinton and her campaign argue that the Vermont senator hasn’t undergone the kind of scrutiny that Clinton and Trump have — and that his poll numbers are over-inflated compared to candidates who have faced intense political attacks from the other party.

The data remain unequivocal, however: The latest averages from HuffPost Pollster give Clinton a just less-than-2-point advantage over Trump, while Sanders — who is virtually certain to finish well behind Clinton in pledged delegates — leads Trump by 10 points. Trump has narrowed Clinton’s lead by 5 points since the end of April, while he’s only chipped 2 points off Sanders’ edge.

Moreover, there’s evidence that Clinton will face challenges uniting Democrats the way Trump has brought Republicans together since eliminating his opponents. Sanders’ backers appear increasingly hostile to Clinton, polls show — especially those voters who currently favor Sanders over Trump but say they would defect to the Republican if Clinton is the Democratic nominee.

The debate isn’t just academic. Part of Sanders’ last-ditch argument to the unpledged superdelegates he’d need to win over to have any hope of winning the Democratic nomination is that they should consider which candidate would run best against Trump before making their choice.

“Virtually every poll taken in the last two months has me doing better against Trump than Hillary Clinton,” Sanders said on CNN on Sunday.

Clinton and her campaign have dismissed that argument repeatedly over the past few months, maintaining that Sanders hasn’t been assailed as Clinton has. Clinton hasn’t gone negative on Sanders with paid media thus far — and with the former secretary of state poised to emerge as the pledged-delegate leader at the end of the voting next month, it’s unlikely Sanders will be the subject of attack ads over the next three weeks.

“I don’t think he’s had a single negative ad ever run against him,” Clinton said Sunday on NBC’s “Meet the Press.” “And that’s fine. But we know what we’re going into, and we understand what it’s going to take to win in the fall.”

Three polls conducted last week confirm Sanders’ advantage in the general election: An NBC News/Wall Street Journal poll released on Sunday showed Clinton leading Trump by 3 points, 46 percent to 43 percent. Sanders, on the other hand, had a commanding 15-point advantage, 54 percent to 39 percent.

Last week, a Fox News poll showed Clinton trailing Trump by 3 points, but Sanders ahead by 4 points. A CBS News/New York Times poll was better for Clinton, showing her leading Trump by 6 points. But Sanders was 13 points clear of Trump, that survey showed.

Some pollsters, in fact, aren’t even asking about a potential Sanders-Trump matchup. An ABC News/Washington Post poll out this weekend didn’t include Sanders in the general-election trial heats. The poll matched Clinton against Trump — showing Trump leading Clinton among registered voters, 46 percent to 44 percent — then added a hypothetical three-way race including 2012 GOP nominee Mitt Romney as an independent candidate.

The ballot test isn’t the only survey data point pointing to Sanders’ strong position — and the shortcomings of both Trump and Clinton. According to HuffPost Pollster, Sanders’ average image rating stands at 50 percent favorable and 41 percent unfavorable. That’s far better than the historically poor ratings for Trump (39 percent favorable/57 percent unfavorable) and Clinton (41 percent favorable/55 percent unfavorable).

Clinton has one distinct advantage over Sanders: More Democrats want her to be the party’s nominee — a finding reflected not just in election returns over the past five months, but also in more recent national polling. Clinton has a 12-point lead in the latest polls measuring the preferences of Democrats nationally.

But, increasingly, there are warning signs that Clinton could struggle to bring those Sanders supporters into the fold. While about two-thirds of Sanders backers in the NBC News/Wall Street Journal poll say they would vote for Clinton over Trump, Clinton’s image rating stands at only 38 percent positive/41 percent negative.

And last week’s NBC News/SurveyMonkey poll — an online, large-sample survey that allows for analysis of smaller subgroups — profiles the small-but-significant pool of voters who are choosing Sanders over Trump, but defect to Trump over Clinton.

The data suggest it will be difficult for Clinton to win them over: Ninety-one percent of these Sanders-Trump voters have an unfavorable opinion of Clinton — including a staggering 73 percent who have a strongly unfavorable opinion.

Democrats are adamant that Clinton will be able to unify the party after she clinches the nomination. Democratic pollster Geoff Garin, who is advising the pro-Clinton super PAC Priorities USA, told POLITICO last week that “it’s certain that Clinton would benefit from putting the intraparty divisiveness behind her in the same way that Trump has benefited from that on his side.”

But it’s not clear that Clinton has the room to grow that Trump did after he knocked out his GOP rivals: Trump is managing to win from 80 percent to 90 percent of self-identified Republicans in the polls, roughly equal to Clinton’s share of the Democratic vote. Sanders isn’t beating Trump because he’s winning more Democrats; polls show he’s winning over more independents and even a few Republicans.

Still, Trump has mostly unified the GOP against steep odds. Even as late as the Indiana primary earlier this month, 42 percent of GOP primary voters said they would be “scared” or “concerned” if Trump were elected president. And a number of prominent Republicans — including House Speaker Paul Ryan — still haven’t expressed public support for Trump’s candidacy.

For Democrats, pre-election surveys and exit polls alike have shown a greater inclination for unity than their Republican counterparts. But as Sanders continues to press his argument — and Trump runs neck-and-neck with Clinton — the process of bringing Sanders voters into the fold becomes more difficult for Clinton as she seeks to reclaim her polling lead over Trump headed into the summer.