As successful as he’s been, billionaire hedge fund manager Bill Ackman has had a few public missteps over the past few years. Most notably, Ackman was a major supporter of Valeant Pharmaceuticals Intl Inc (NYSE:VRX). Ackman’s Pershing Square Holdings lost billions as VRX shares plunged from an all-time high of $263 to just $14 at the beginning of the year.

Ackman also took a 9.9% stake in Chipotle Mexican Grill, Inc. (NYSE:CMG) last year, after a norovirus scare tanked the stock. That contrarian bet looked like a smart play, with CMG nearing $500 just a few months ago. But a weak earnings report and more rumors of health concerns have sent CMG back to a four-year low near $300.

To be fair, Ackman has had some big winners as well — even if they don’t get quite the same publicity. Burger King owner Restaurant Brands International Inc (NYSE:QSR) has gained nicely, and the long-term track record of Pershing Square remains one of the most impressive in the industry.

But Ackman’s most well-known position has been his short in Herbalife Ltd. (NYSE:HLF). So far, that position has been a disappointment — and a very public one at that.

And as Herbalife itself and major shareholder Carl Icahn both try and “squeeze” Ackman and Pershing Square, it’s worth wondering if, and when, Ackman might finally throw in the towel on HLF stock.

‘Betting on Zero’ In HLF

Bill Ackman’s thesis on Herbalife is rather simple. He has argued that the company is purely a pyramid scheme, and should be shut down by the FTC. That in turn, as Ackman reiterated in last year’s shareholder letter would value Herbalife shares at zero. And it would result in huge gains for Ackman’s $1 billion short position in HLF.

It’s been the most public of Pershing Square’s positions by design, but it hasn’t worked. Ackman gave a major presentation in late 2012 making his short case and cooperated on the documentary “Betting On Zero,” which was released earlier this year. The idea was that regulators would listen and eventually shut Herbalife down.

That hasn’t happened. An FTC settlement last year cost Herbalife $200 million and required changes in its business model. But the result wasn’t what Ackman sought — and it wound up moving Herbalife stock higher.

The question now becomes: what’s left for Ackman to do? Herbalife continues to expand internationally, but one imagines a U.S.-based hedge fund manager has little pull with regulators overseas.

The company seems to have adapted well to the new FTC rules. And in the meantime, Ackman’s very public bet against Herbalife has made him a target.

The Battle Over Herbalife Stock

Not long after Ackman disclosed his short position, noted investor Carl Icahn acquired 13% of Herbalife and so began a public battle between the two billionaires.

Ackman’s position left him vulnerable to a short squeeze, in which shorts either can’t find shares to buy back to cover their positions — or, at least, are left facing higher borrow rates. And Icahn, who has increased his holdings to 24% since, seemed to revel in creating just such a squeeze on Ackman.

Now, Herbalife itself is doing the squeezing. A tender offer announced last week means the company will repurchase roughly 10% of its outstanding shares, depending on the final price offered. That’s a big problem for Ackman.

As Business Insider reported, the buyback itself could squeeze Pershing Square’s position. If the shareholders currently lending their shares to Ackman, in turn, sell them to Herbalife, Ackman will have to find new shares to borrow or new shares to buy.

Finding shares to borrow may be difficult and expensive. Financing costs alone could blow out Ackman’s position. The only other alternative, however, would be to cover the position at a loss.

Will Ackman Give In?

So will Bill Ackman give in? Only he knows. But it’s not at all impossible. Herbalife’s tender offer will leave Ackman trying to short the stock almost by himself. At the least, it will make him even more vulnerable to another squeeze — a fact Carl Icahn will know all too well.

Meanwhile, the moral aspect of Ackman’s crusade appears at an end. The FTC has spoken, whether the fund manager likes it or not. Ackman told The New Yorker earlier this year that he had considered abandoning his short back in 2014 before the FTC announced its investigation of Herbalife. He’s no doubt considering doing so again. And this time, he simply may have no other choice.