I wonder if there’s a part of Bill Clinton that doesn’t really want Hillary Clinton to become president, particularly if she has to distance herself from his legacy to do so. How else to explain why one of the world’s most talented and agile politicians is so consistently flat-footed and destructive when advocating on his wife’s behalf? How else to explain his terrible and destined-to-be-viral confrontation Thursday with Black Lives Matter protesters in Philadelphia?

It started when the demonstrators interrupted Bill Clinton’s speech to protest his draconian 1994 crime bill, which, among other things, expanded the scope of the death penalty, enshrined “three-strikes” provisions into federal law, and allocated almost $10 billion in funding for prison construction. That bill is now widely seen as contributing to the human catastrophe of mass incarceration. Hillary Clinton is proposing a diametrically different approach to criminal justice, and even Bill Clinton renounced the law last year, though today, bafflingly, he went back to defending it.

“I don’t know how you would characterize the gang leaders who got 13-year-olds hopped up on crack and sent them out into the street to murder other African American children,” he shouted at the protesters. “Maybe you thought they were good citizens. She didn’t. She didn’t! You are defending the people who kill the lives you say matter.” The crowd cheered, but most Hillary supporters who watch it online will be aghast, if only out of political self-interest. Right-wing outlets like the Daily Caller and the Weekly Standard rushed, naturally, to post video of Bill’s hectoring.

At a time when Hillary Clinton is dependent on black voters and campaigning with mothers who’ve lost sons to police violence, Bill Clinton yoked her to his own discredited policies. He reminded everyone that, in defense of his bill, she’d once spoken about underage “superpredators,” language she has since apologized for. Then, Bill Clinton aped the maddening right-wing tendency to derail conversations about criminal justice abuses by invoking black-on-black crime. He might as well have said, “All lives matter!”

It was a mess, but it’s not the first mess he’s caused for his wife’s campaign. Just a couple of weeks ago, he decried “the awful legacy of the last eight years,” which sounded a lot like a condemnation of the Obama presidency—a presidency that Hillary Clinton is doing her best to tie herself to. And in February, Clinton said that if the system is rigged, it’s because Americans “don’t have a president that’s a changemaker.”

One might attribute this repeated clumsiness to the fact that Bill Clinton is getting old; his hearing is bad, and on the trail he looks frail and wan. Perhaps he’s simply slipping, mentally. But let’s remember that Clinton caused similar problems for Hillary in 2008. There was the time he tried to diminish Obama’s victory in South Carolina by noting that Jesse Jackson won there as well. The time he described the idea that Obama had gotten the Iraq war right as “the biggest fairy tale I’ve ever seen.” The time—it hurts to remember it—when he complained that the Obama campaign “played the race card on me.”

And yet, after all that, once Hillary had lost and Bill Clinton was supporting Obama, the sloppiness ceased and he was back to performing superbly. (Witness, for example, his celebrated speech at the 2008 Democratic convention.) It is somehow only when he is working on his wife’s behalf that he veers into sabotage. What is needed here is probably a shrink, not a neurologist. Either he doesn’t want her to overtake him, or he doesn’t want her to repudiate him. Regardless, Hillary should shut him down. She can’t divorce him, but she can fire him.

Read more Slate coverage of the Democratic primary.