"Never Trump" Republicans aren’t giving up in their quest to find a conservative alternative to Donald TrumpDonald TrumpFive takeaways from the Ohio special primaries Missouri Rep. Billy Long enters Senate GOP primary Trump-backed Mike Carey wins GOP primary in Ohio special election MORE.

Now that Trump has cleared the field of rivals to become the GOP's presumptive presidential nominee, anti-Trump conservatives have turned their attention to recruiting a candidate to challenge Trump and Democratic front-runner Hillary ClintonHillary Diane Rodham ClintonFive takeaways from the Ohio special primaries Shontel Brown wins Ohio Democratic primary in show of establishment strength READ: Cuomo's defense against sexual harassment investigation MORE in the general election, either as an independent write-in candidate or as part of a third-party campaign.

Speaker Paul RyanPaul Davis RyanTo cut poverty and solve the labor shortage, enhance the Earned Income Tax Credit Wisconsin GOP quietly prepares Ron Johnson backup plans RealClearPolitics reporter says Freedom Caucus shows how much GOP changed under Trump MORE’s (R-Wis.) decision Thursday to not endorse Trump will only give further oxygen to the furious efforts by some to find a Trump alternative.

The Hill interviewed several operatives associated with the anti-Trump movement to ask who they’d like to see run.

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Here’s who they hope to see on the ballot.

Mitt Romney

The 2012 GOP nominee first declined to run for president in January of 2015. 

Since then, he’s consistently beat back pleas from panicked establishment Republicans to return to the fray and save the party from Trump.

The announcement Thursday from Ryan, Romney’s 2012 running mate, that he’s not ready to back Trump will surely fuel rumors that the former Massachusetts governor could get back in the ring.

In many ways, Romney would be the dream anti-Trump recruit.

He would have instant access to a national fundraising network and enough name ID to move quickly up the polls and make the debate stage.

Romney’s entrance would attract a media frenzy, and he’s the kind of center-right candidate that Republicans opposed to Trump could feel good about voting for.

Romney has thoroughly rebuked Trump and campaigned against him at every turn. 

He has said that he will write a name in if his options are down Trump and Clinton. Could that be his name?

Sen. Ben Sasse (R-Neb.)

The 44-year-old freshman senator from Nebraska has been one of the most vocal opponents to Trump on Capitol Hill.

On Thursday, Sasse penned an open letter on his Facebook page about why voters should not settle for either Trump or Clinton and outlined the qualities he wants to see in an independent or third-party candidate.

“Why are we confined to these two terrible options?” he wrote. “This is America. If both choices stink, we reject them and go bigger. That’s what we do.”

Unfortunately for anti-Trump conservatives, Sasse, who has a young family, says he won’t run himself.

Anti-Trump Republicans are holding out hope he’ll reconsider. Three different people mentioned his name to The Hill on Thursday.

General John Kelly

Anti-Trump conservatives spent months trying to convince Gen. James “Mad Dog” Mattis, a revered, straight-talking four-star retired Marine Corps general, to launch an independent bid.

Mattis officially took his name out of the running last week.

Now they have their eyes on another tell-it-like-it-is military man: Former U.S. Marine Corps Gen. John Kelly.

Kelly retired in January after more than four decades of service. He spent years in various leadership posts in Iraq and lost a son, former Marine Robert Kelly, to combat in Afghanistan.

Kelly has not spoken publicly about the presidential race, and a spokesperson did not return a request for comment about whether he’d be interested.

Former New Mexico Gov. Gary Johnson

The likely Libertarian Party nominee is so far the only candidate other than Trump and Clinton who could be on the ballot in all 50 states.

Johnson served two terms as the Republican governor of New Mexico beginning in 1995. He participated in one GOP presidential debate early in the 2012 cycle before running as a Libertarian and winning about 1.3 million votes in the general election.

Since 2012, Johnson has been working as president of a marijuana marketing firm. He left that position to run for president, winning the Libertarian nomination again in 2016. 

One of the biggest challenges facing a new candidate will be hitting the threshold of 15 percent in national polls to qualify for the debates.

Johnson could be the answer: A Monmouth University survey from late March found him taking 11 percent in a hypothetical match-up against Trump and Clinton.

In a statement released Wednesday after Sen. Ted CruzRafael (Ted) Edward CruzUp next in the culture wars: Adding women to the draft Biden's bipartisan deal faces Senate gauntlet 228 Republican lawmakers urge Supreme Court to overrule Roe v. Wade MORE (R-Texas) left the GOP race, Johnson put himself forward as the alternative to “two of the most polarizing candidates in recent history.”

“With millions of Americans now feeling politically ‘homeless,’ a two-term Governor who balanced budgets, cut taxes, cut regulations and truly reduced the size of government may offer the home they are seeking,” Johnson said.

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Rep. Justin AmashJustin AmashKamala Harris and our shameless politics Amash warns of turning lawmakers like Cheney into 'heroes' Cheney set to be face of anti-Trump GOP MORE (R-Mich.)

The 36-year-old libertarian-leaning Michigan lawmaker says he’ll never support Trump and is furious with colleagues who have warmed to the likely nominee in recent weeks.

Amash, who first backed Sen. Rand PaulRandal (Rand) Howard PaulFive takeaways from the Ohio special primaries Trump-backed Mike Carey wins GOP primary in Ohio special election Hillicon Valley: Senate report finds major cyber shortcomings in federal agencies | Gig firms seek Mass. ballot question to classify workers as contractors | Blizzard's president steps down after workplace protests MORE (R-Ky.) in the primary and later Cruz, has thrived on Capitol Hill as a wildcard willing to buck GOP leaders.

He stoked speculation that a third-party run may be in the works with a cryptic tweet sent out late Tuesday night after Cruz suspended his campaign. 

Amash did not return a request for comment.

Former Sen. Tom CoburnThomas (Tom) Allen CoburnNSF funding choice: Move forward or fall behind DHS establishes domestic terror unit within its intelligence office Wasteful 'Endless Frontiers Act' won't counter China's rising influence MORE (R-Okla.)

Coburn served three terms in the House followed by two in the Senate, cutting his final stint short after being diagnosed with cancer.

Healthy now, Coburn is on the short list for most anti-Trump Republicans.

The Oklahoma Republican, who backed Sen. Marco RubioMarco Antonio RubioRubio presses DNI to investigate alleged unmasking of Tucker Carlson Senate holds sleepy Saturday session as negotiators finalize infrastructure deal Break glass in case of emergency — but not for climate change MORE (R-Fla.) in the primary, told The New York Times earlier this year that he’d back a third-party bid to stop Trump. 

Coburn said he didn’t expect that he would be that candidate, but he also declined to rule it out.

Coburn is well-known inside Washington from his frequent appearances on the cable news circuit. He's quotable and has a reputation as a pragmatic conservative.

But some believe he lacks the name recognition and a national fundraising network to get off the ground.

Nikki Haley

The South Carolina governor is one of the brightest young stars in the Republican Party.

Several anti-Trump conservatives have dropped her name, and the reasons are clear: As an Indian-American woman, she provides a double-shot of diversity. She’s also telegenic, charismatic and one of the most popular governors in the country.

Haley said Wednesday she’d support the GOP nominee, but she could come under pressure to challenge him instead.

Sen. Rand Paul (R-Ky.)

The former “most interesting man in politics” could reclaim that title with a bold move back into the presidential race.

He’d likely find the press eager to cover his bid this time, giving him a platform to get out his message of expanding the party. That message was drowned out last year in the crowded GOP primary.

Conservative blogger Erick Erickson, a prominent “Never Trump” voice, told The Hill on Thursday that Paul would be a “viable” contender as a third-party or independent candidate.

The Kentucky GOP made it so that Paul could run for both president and reelection to the Senate simultaneously. But Paul's reelection bid is now in full-swing, and it would irritate many in the party if he were to distract himself from that with another long-shot presidential bid.