After 25 years of Republicans attacking Hillary Clinton, there are few new lines on any number of fronts but their nominee, Donald Trump, has found a new one: Claiming that she doesn’t have the mental or physical stamina to be president.

At a rally in Youngstown, Ohio, last week he proclaimed that Clinton lacks the “mental or physical stamina to take on ISIS.” He repeated the claim this weekend, asking on Twitter: “#Where’sHillary? Sleeping!!!” His surrogates have gone the next step, not only questioning her stamina but floating conspiracy theories about her physical health.

The idea seems to be that if Clinton isn’t at a public event, she’s slacking off; this exposes his biggest weakness as a candidate: In his mind, unless you’re doing big rallies, you’re not working at all.

It doesn’t seem to occur to Trump that Clinton could be reading through policy briefings, writing speeches, filming TV commercials, doing debate prep or any number of activities that a thoughtful, smart candidate would engage in—especially in the quieter month of August. For him, it’s narcissistic, nationalistic celebrations of his candidacy or nothing.

Beyond that, here’s why this attack won’t work: It’s Clinton’s incredible mental and physical stamina that has frustrated Republicans for 25 years. It is her strength and resilience that have driven them absolutely nuts. I imagine them asking themselves: “How is she still here?”

For years, people have said that it is her ambition that most inspires her detractors to attack her. I disagree. Clinton’s biggest sin in the eyes of her opponents is not that she is ambitious; it is that she dares to get back up after she is knocked down.

There’s nothing less attractive to the patriarchy than resilience in the face of authority that allows women to have their ambition as long as they submit when corrected.

So the fact that she keeps getting back up, time after time, is jarring to folks who think that they’ve finally found a way to put her away for good.

Every time the GOP thinks they’ve found a way to finally knock her down, they’re almost gleeful. We saw this most recently with the Benghazi hearings, with how eager Rep. Trey Gowdy was to be the one to finally end her career, but as we saw she calmly and crisply replied to 11 hours of questioning without missing a beat. When he finally released his report, Gowdy had nothing to offer after spending millions of taxpayer dollars.

Republicans keep failing in their quest to knock her down and keep her down because while she has, admittedly, made mistakes, there is no there there.

The only person who has cracked any code is Hillary Clinton. She resigned herself long ago to the fact that she would continually be knocked down and that her job is to not try to avoid being knocked down, but to always get back up.

As Trump and his supporters have finally begun to digest that he is heading toward an unprecedented loss they have become desperate enough to lob accusations at her that even her most strident enemies hadn’t had the audacity to propose. And yet, she’s still here, doing the smart, quiet work she’s always done.

Some have suggested that Clinton in turn question, in a conspiratorial way, Trump’s physical and mental stamina. But she’s too smart to do that, she knows that when she attacks Trump she can quote him, while he has to resort to coming up with an interpretation of her intentions.

If he doesn’t have a leg to stand on now, how could he possibly handle the religious, oil-fueled might of terrorists who won’t be horrified by his tweets but emboldened by them?