As Senator Bernie Sanders’s lead in the Democratic presidential primary has solidified this month, some major Democratic donors have started funneling their money into an effort to thwart the rise of the self-described democratic socialist. But even some of the donors involved in the attempt to stop Sanders concede it may be too late.

Major donors and strategists worry the fractured field of Democratic candidates going into Super Tuesday will split up the delegates and funding necessary to block Sanders from running away with the nomination. “Democrats who fear that Bernie Sanders would likely lose to Trump are frustrated that the crowded field of moderates in the race is making it difficult for one to break out of the pack,” says Jon Cooper, a Democratic donor supporting former Vice President Joe Biden, who thinks other candidates should exit the race.

In the aftermath of the New Hampshire primary, more than half a dozen donors turned to Jonathan Kott, a former longtime aide to West Virginia Democratic Sen. Joe Manchin. “A lot of Democrats were surprised that Bernie Sanders had been able to avoid the scrutiny of a front runner,” Kott says, “and they decided to act and make sure voters had all the information about his radical views before they voted.”

Kott formed the Big Tent Project, a group which, as a 501(c)4 nonprofit, does not have to disclose its donors. Within days the group received more than $1 million, which it poured into ads in Nevada and South Carolina to sow doubt about Sanders’ ability to deliver on his policy platform. “Socialist Bernie Sanders promises the world,” stated one ad that aired in both states. “But at what cost? $60 trillion.” Donations to the group picked up even more after Sanders’ win in Nevada on Feb. 22, according to Kott, who says he’s steadily been receiving more six- and seven-figure donations and is closing in on $3 million.

But the investment is minuscule in a race that features two billionaire candidates burning through hundreds of millions of dollars. And so far it has done little to stop Sanders’ ascent. Although there are plans to expand the ads in at least some of the 14 states voting on Super Tuesday, the contests are days away, with Sanders projected to win the most delegates. And while no one is yet conceding defeat, donors and strategists say the factor that aided Sanders’ lead in the first place—a crowded field of moderate alternatives—is continuing to complicate the effort.

The remaining candidates who are not funding their own campaigns—Biden, former South Bend, Indiana Mayor Pete Buttigieg, Minnesota Sen. Amy Klobuchar and Massachusetts Sen. Elizabeth Warren—are splitting both delegates and money from donors, allowing Sanders to build on his advantage. In Iowa, New Hampshire and Nevada, Sanders amassed 45 pledged delegates of the allocated 100, while the other four split the remaining 55. Sanders, known for his small-dollar fundraising capabilities, raised more than $25 million in January, according to filings with the Federal Election Commission. Biden, Buttigieg, Klobuchar and Warren each raised less than that individually, but amassed nearly $32 million combined.

“There are so many people in the race that the vote that isn’t Bernie is being split five or six ways,” says Alix Ritchie, a Democratic donor worried about Sanders’ chances against President Donald Trump. “He’s winning more votes than any individual person because [they are] splitting the rest of the vote.”

Ritchie herself has donated to Biden, Buttigieg, Klobuchar and Warren this cycle, and now admits that casting such a wide net has become part of the problem. “There are many people I know who have donated to several candidates who aren’t Bernie,” she says. “Everybody is just hoping someone rises above the crowd and they can get behind.”

Which highlights the most immediate problem facing the Democratic donors and operatives who want to stop Sanders. Cooper, for instance, thinks everyone but Biden should exit the race, because Biden polls the best against Trump in battleground states. But others reject the idea agree that candidates who have performed better than Biden to date should be the ones to exit the race.

Ami Copeland, who was deputy finance director for Barack Obama’s 2008 presidential campaign, believes donors would have rallied behind a single moderate candidate earlier if one stood out from the pack. “Each has their strengths and their weaknesses, and that is reflected in their appeal to the larger donor base,” he says. “Unfortunately that continues today.”

Rufus Gifford, a Biden fundraiser, says there is still time for the party to unify around a Sanders alternative.”When it becomes clear what the Bernie alternative is, you’re going to see the donor community – both high dollar and grassroots – coalesce around that person,” he says.

But the fear among some Democratic donors and strategists is that there won’t be any real clarity before Sanders’ delegate lead becomes insurmountable. There are few signs any candidate will get out before Super Tuesday, which will award more than a third of the total delegates to the party’s nominating convention in Milwaukee this summer. And despite donors’ fresh injection of funds, that fractured dynamic seems to be accomplishing what that money is working to stop: Sanders’ march to the nomination.

“Every day,” says Copeland, the Obama fundraiser, “it gets harder and harder.”

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Write to Alana Abramson at Alana.Abramson@time.com.