I can’t imagine that Bernie Sanders actually expected to topple Hillary Clinton. Sure, he expected to change the parameters of debate and offer a broader vision of the Democratic Party, but not to run away with it. That he might succeed says less, I’m afraid, about Sanders than about Clinton. Friends of Clinton say she’s wonderful company in private, and supporters say she’s at her best when governing rather than campaigning. But that doesn’t get anyone very far. They might as well be saying she’s great company when no one’s around, and she’s a great candidate when no one else is running.

On Sunday, we’ll get the best indication yet of whether Bernie Sanders really intends to go all the way. He has never gotten rough, sticking to a mode of “implied contrast” on issues. Yet even his mildest jabs have wounded the frontrunner—or erstwhile frontrunner—as if a tug on her sleeve would be enough to rip off her entire arm. Last November, when Sanders told the Wall Street Journal that his political consistency on a trade deal (with an implied contrast to Clinton’s reversals) “does speak to the character of a person,” the Clinton campaign reproached the Sanders campaign for “personal attacks that they previously said he wouldn’t do.”

Sanders prides himself on never having run a negative ad (a claim Clinton’s touchy campaign disputes), but he’s perfectly capable of negative statements. He has called Donald Trump “a pathological liar” who “simply cannot control himself,” someone who “lies, lies and lies again.” Not so much implied contrast there. The question, as Ross Douthat notes in The New York Times, is whether Sanders is willing to deploy even a fraction of such vehemence against his Democratic rival.

It can’t be an easy choice. First, Sanders must decide if he can really withstand the hell of an entire presidential campaign, possibly against Donald Trump, and then becoming America’s oldest president-elect, at age 75. True, the Oval Office will not turn Sanders’ hair gray, but the experience of the presidency, the position of sudden world-spanning power, is extreme. So is the confidence that it requires.

Then Sanders must assess whether he can win a general election. He leads several Republican candidates in head-to-head polling; it’s not impossible. But Sanders would be as far to the left as anyone nominated by the Democratic Party since George McGovern, and national-security worries are running high. Attacks by someone like Donald Trump would also be bruising. Already, Trump has called out Sanders for weakness, harping on a Seattle appearance in which Sanders relinquished his microphone to protesters. The accusations of softness would be persistent.

Finally, and perhaps most important, Sanders must decide if he can tolerate the risk of leaving Clinton bloodied as she heads into the general election. He has several possible lines of attack from which to choose: judgment, character, policy differences. But many of them would leave her even more vulnerable to defeat in November, were she to become the Democratic nominee. Laxity with regulation and security (that is, the email problem), intervention in Libya, the Iraq War authorization, coziness with Wall Street donors—all of these could draw plenty of Clinton blood, but Republicans would take pleasure in recycling many of them, citing Bernie as an ally. And Sanders really, really does not want to see President Trump.

Maybe Sanders can hold off on his choice a little longer. Maybe he’ll decide to take out the hammer only if he wins Iowa and New Hampshire. But maybe not. I think we’ll see some pretty clear indications on Sunday night. We can say this much, though: if Hillary Clinton felt that going nuclear on Sanders would help her campaign, she would do it. Obama’s people will not soon forget the 2008 primaries, when Clinton said, “Senator McCain will bring a lifetime of experience to the campaign; I will bring a lifetime of experience; and Senator Obama will bring a speech that he gave in 2002.” That made it into a McCain advertisement later that year.

And yet we know what happened, despite all the nastiness. Obama won handily anyway. Does that help you with your decision, Senator Sanders? Yeah, I didn’t think so.