Efforts by disgruntled Republicans to launch a third-party challenge to presumptive presidential nominee Donald Trump are likely to fail, the victim of a waning clock and the Herculean effort it takes to get a third-party candidate on the ballot.

Despite the long odds, Republicans who feel that the unconventional and unpredictable Trump isn’t a true conservative have ramped up discussions on trying to defeat him and Democratic presidential front-runner Hillary Clinton in November with an alternative candidate who hews closely to their political beliefs.

“Why are we confined to these two terrible options?” Sen. Ben Sasse, R-Neb., wrote Wednesday in a lengthy Facebook post critical of Trump and Clinton. “Why shouldn’t America draft an honest leader who will focus on 70 percent solutions for the next four years? You know — an adult.”

Republican anti-Trump forces are hunting for a willing candidate, seeking out potential donors, and mapping out legal strategies to navigate the myriad of often-stringent state rules and regulations to get a third-party candidate on the ballot.

“It’s basically really, really late in the game to get onto the ballot,” said Elaine Kamarck, founding director of the Center for Effective Management at the Brookings Institution. “Almost all of these states have signature requirements. Even if you hire professional, door-to-door types, you can’t do this quickly. Imagine organizing 80,000 signatures. And they have to be real, living, registered voters.”

Still, names of potential third-party candidates have been bandied about: Sasse, former Massachusetts governor and 2012 Republican presidential candidate Mitt Romney; former Texas Gov. Rick Perry; former Secretary of State Condoleezza Rice; former Sen. Tom Coburn, R-Okla.; retired U.S. Marine Corps General James Mattis; and Republican Govs. Susana Martinez of New Mexico, Brian Sandoval of Nevada, and Nikki Haley of South Carolina.

So far, no one is jumping at the chance to jump into the race. That’s probably because no independent candidate has ever won the presidency, and some have gone down in history as spoilers.

Texas tycoon H. Ross Perot got 19 percent of the vote in his 1992 independent bid, which many say took votes away from incumbent Republican President George H.W. Bush and helped elect Democrat Bill Clinton.

Some Democrats blame consumer advocate Ralph Nader’s independent run in 2000 for Vice President Al Gore’s narrow loss to George W. Bush.

“It’s an uphill climb — everybody recognizes that, regardless of the route we go — but there are a lot of Republican donors sitting on the sidelines who would rather fund a third party than fund Donald Trump,” Erick Erickson, a conservative talk radio host and writer who’s leading third-party conversations, told The Hill newspaper.

Trump and Republican National Committee officials dismiss the third-party quest as Washington cocktail conversation, a political pipe dream from party members who are unhappy now but will eventually return to the tent rather than face the prospect of a Hillary Clinton presidency.

“It’s not going to happen,” Sean Spicer, the RNC’s communication’s director, said on CNN Thursday. “There is no organization, no funding mechanism, and frankly, there’s no consensus candidate.”

Then there’s the rapidly narrowing window for getting a candidate on state ballots and getting the various wings of the party to agree on a consensus candidate at this late date.

For example, Monday is the deadline for an independent to file a declaration of candidacy in Texas. The application must be accompanied by a petition signed by at least 79,939 registered voters who didn’t vote in the presidential primary of either party.

And the candidate must have a running mate picked. The application requires signed consent from the candidate’s vice presidential choice, according to the Texas secretary of state’s website.

North Carolina has a June filing deadline and requires signatures of registered voters equal to 2 percent of the total number of voters who cast ballots in the most recent gubernatorial general election — or a total of 89,366 signatures.

A petition must also be signed by at least 200 registered voters from each of the state’s 13 congressional districts.

The filing deadline for independent and third-party candidates in Florida and South Carolina is July 15; Illinois; Missouri, Kansas and Pennsylvania, Aug. 1; California, Aug. 12; Kentucky and Mississippi, Sept. 9.

“The irony, of course, is that the major parties have always tried to find ways to close third parties out so it’s particularly difficult to get on the ballot,” said Daniel Franklin, associate political science professor at Georgia State University. “So they’re kind of being hoisted by their own petard. It’s very difficult for third parties to get on the ballot, particularly in Texas.”

But even with the tight deadlines and signature challenges, Kamarck said there is another avenue for a third-party candidate to get on the ballot. Rather than start from scratch, an anti-Trump Republican alternative candidate could run under the banner of an already-existing party.

“There are a handful of these that do in fact manage well enough year-to-year to have a ballot slot” in some states, she said. “But they have conventions, too, where they nominate their candidates for president. You’d have to convince them to let you get on their line.”

In March, Franklin, a former Texas resident, thought the environment was right for a third-party presidential run, saying “The last time something like this happened was in 1948 when the ‘Dixiecrats’ bolted and (former Vice President) Henry Wallace ran from the left.”

Now, he thinks it’s too late for anti-Trump Republicans to mount a viable third-party campaign.

“The problem that a third party would have is getting on the ballot,” he said. “And I think the Republicans are now concerned about their down-ticket (Senate and House) races and it might make the ballot a little confusing. But I think the main problem is that it’s too late. They would have had to make their plans a month and a half ago.”