Senator Elizabeth Warren has made it abundantly clear that she is not running for president. Not now. Not in the future. Still, that message hasn’t sunk in with progressives eager to see her in the White House. “As this race gets underway,” Ready for Warren campaign manager Erica Sagrans wrote in an email Wednesday, “we're more energized than ever about the possibility for Warren getting in the race, and we're stepping up our efforts to convince her to run.”

Eventually, Sagrans and company will have to admit that Warren isn’t running for president. Until then, the next best thing is a reality: a Bernie Sanders presidential run. The Vermont senator is announcing his presidential run on Thursday, a move that rightly ought to thrill Warren fans. Instead, their happiness is tempered. Warren and Sanders may appeal to the same constituency but only one could have a legitimate shot at winning the Democratic nomination—and the left knows it.

Warren and Sanders don’t differ much on policy. Both have led the fight against President Barack Obama’s trade deal, the Trans Pacific Partnership. “This is your Capitol,” Sanders told a crowd of labor and environmental activists at a rally against the TPP a few weeks ago, “and not just the Capitol of the billionaire class.” Only Warren received louder cheers. Both are adamant opponents of big Wall Street banks and support breaking them up. In fact, Sanders, a self-described socialist, is to the left of Warren and rails against big moneyed interests on issues including campaign finance reform and climate change. If voters on the left want a diehard liberal to challenge Hillary, they couldn’t do much better than the man who called for “a moral and political war against the billionaires and corporate leaders, on Wall Street and elsewhere.”

Naturally, the unaffiliated left is excited that Sanders is running. “MoveOn members have cheered on Sen. Sanders for years as he's stood up to the Wall Street banks and wealthy interests who have rigged the game in Washington and knee-capped our country’s middle-class and working families,” Anna Galland, the executive director of MoveOn.org, said in a statement. Adam Green, the co-founder of the Progressive Change Committee, echoed the enthusiasm: “The goal of many progressives in 2016 is to ensure that the election is fought over big, bold, economic populist ideas. Bernie Sanders will certainty help pull the debate in that direction, and he's a positive addition to the race."

Yet they still long for Warren to enter the race. “We and our allies continue to call on Sen. Elizabeth Warren to also bring her tireless advocacy for middle-class and working Americans to the race,” Galland said. “Our country will be stronger if she runs.” Why do liberals still yearn for a Warren campaign, with Sanders in the game? Electability. The left doesn’t believe that Sanders can top Clinton, whereas Warren just might. “We need Senator Elizabeth Warren in the race to make sure we have a Democratic nominee who will lead these fights all the way to the White House,” said Ready for Warren’s Erica Sagrans. Sanders, by implication, is not that nominee.

That analysis is correct. Sanders doesn’t have Warren’s charisma or her fundraising base. The “Run Warren Run” Facebook page has ten times more likes than the “Ready for Bernie” page. Her national profile far exceeds his. Among the chattering classes, Warren would be a serious challenger to Clinton. Sanders isn’t.

Sanders’s best-case scenario goes something like this. Clinton comes out in favor of the TPP and the fast track authority that makes it easier to pass the trade bill, infuriating unions that consider trade a top issue of the Democratic primaries. In a major address on the 2016 race Tuesday, AFL-CIO President Richard Trumka said, “We expect those who seek to lead our nation forward to oppose fast track. There is no middle ground, and the time for deliberations is drawing to a close.” That is a clear message to Clinton: Oppose the trade deal or else. Bernie Sanders could be that else, if not as a bona fide threat to win, at least as an alternative recipient of campaign monies.

But even in that best-case scenario, with labor groups supporting him over Clinton, Sanders has approximately no chance of winning. When I asked Ruy Teixeira, a Democratic strategist, whether that hypothetical could put Clinton’s nomination at stake, he responded, “An easy one: No.”

To be fair to Sanders, he’s not entering the race expecting a victory. Citing “confidants,” the Washington Post reported Tuesday that he was mostly entering the race to participate in the debates. Fair enough. Sanders, not one to pull punches, will certainly try to rough Clinton up in any debates. Maybe he can nudge her to the left, particularly on trade. If that happens, his presidential run will be a success.

For the thousands of liberals dreaming of a Warren presidency, simply pushing Clinton to the left isn’t enough. They want to win; Sanders can’t accomplish that. So the futile campaign to convince Warren to enter the race will continue.

A previous version of this article misspelled the name of Erica Sagrans.