Sen. Ben Sasse (R-Neb.) speaks at the American Conservative Union annual conference in Maryland on March 3. Sasse is being pressured to consider a presidential run. (Gary Cameron/Reuters)

A band of exasperated Republicans — including 2012 presidential nominee Mitt Romney, a handful of veteran consultants and members of the conservative intelligentsia — is actively plotting to draft an independent presidential candidate who could keep Donald Trump from the White House.

These GOP figures are commissioning private polling, lining up major funding sources­ and courting potential contenders, according to interviews with more than a dozen Republicans involved in the discussions. The effort has been sporadic all spring but has intensified significantly in the 10 days since Trump effectively locked up the Republican nomination.

Those involved concede that an independent campaign at this late stage is probably futile, and they think they have only a couple of weeks to launch a credible bid. But these Republicans — including commentators William Kristol and Erick Erickson and strategists Mike Murphy, Stuart Stevens and Rick Wilson — are so repulsed by the prospect of Trump as commander in chief that they are desperate to take action.

Their top recruiting prospects are freshman Sen. Ben Sasse (R-Neb.), a conservative who has become one of Trump’s sharpest critics, and Ohio Gov. John Kasich, who withdrew from the Republican presidential race May 4. Romney is among those who have made personal overtures to both men in recent days, according to several people with knowledge of the former Massachusetts governor’s activities.

This summer's political conventions could get heated – but it certainly wouldn't be the first time. (Peter Stevenson/The Washington Post)

Earlier prospects included former senator Tom Coburn ­(R-Okla.) and retired Marine Corps Gen. James N. Mattis. Former secretary of state Condoleezza Rice and retired Army Gen. Stanley A. McChrystal have been bandied about as potentially potent political outsiders.

The recruiters also delved into the world of reality television for someone who might out-Trump Trump: Mark Cuban, the brash billionaire businessman and owner of the Dallas Mavericks basketball team.

Again and again, though, these anti-Trump Republicans have heard the same tepid response: Thanks, but no thanks.

“I don’t see it happening,” ­Cuban wrote in an email.

Cuban, a cast member on “Shark Tank,” the ABC reality series in which entrepreneurs pitch investors about their business ideas, said his pursuers — he declined to name them — have told him that his “bluster and volume, combined with substance and the ability to connect with voters on a more personal basis,” could make him a winning candidate.

“He could come after me all he wanted, and he knows I would put him in his place,” Cuban said of Trump. “All that said, again, I don’t see it happening. There isn’t enough time.”

To many political professionals, the notion of winning the presidency from outside the two-party system is pure fantasy. Former New York mayor Michael Bloomberg spent considerable time and money studying his chances­ for an independent run only to conclude in March that there was no plausible path.

Further tempering the current talks on the right are fears that an independent conservative candidate could forever be a pariah by splintering the Republican vote and ensuring victory for the Democratic nominee.

“The career of the individual would come to an end, and he would have a difficult spot in history for being responsible for putting Hillary Clinton in the White House,” said Patrick J. Buchanan, a conservative who unsuccessfully ran for president in 2000 on the Reform Party ticket.

Buchanan was dismissive of the current efforts. “These are the mice trying to bell the cat — only they can’t get one mouse to go out and do it,” he said.

Draft promoters have been telling potential candidates that 2016 already has proved to be an unpredictable cycle and that anything could happen, such as Trump’s candidacy shriveling under the expected Democratic advertising assault. What’s more, they tell them, you would have no bigger platform to promote your ideas than in a three-way general election that would attract global attention.

Pollsters have been conducting private surveys over the past week to measure the plausibility of an independent candidate, said three people working closely on the project.

There are formidable logistical hurdles. The deadline to get on the ballot in Texas, which has the second-largest trove of electoral votes, already passed, but organizers said they think a legal challenge there could be successful. Other state deadlines are fast approaching, and many require petitions with thousands of signatures.

Some anti-Trump Republicans are downsizing their ambitions to a more focused, state-specific effort. Murphy, who ran a super PAC for former Florida governor Jeb Bush in his failed 2016 bid, is pushing one such proposal. Murphy envisions an independent candidate on what he termed “an honorable mission” in Colorado, New Hampshire and Ohio — three battleground states with relatively lax ballot-access rules.

“Running an anti-Trump protest candidate in a handful of swing states really appeals to me,” Murphy said. “You could deny Trump the presidency and perhaps help important Senate and other down-ballot races­ by giving another choice to Republican voters who abhor Hillary Clinton and can’t cross the moral line to vote for Trump.”

One related objective is to prevent both Clinton and Trump from clinching a majority in the electoral college and thus throwing the presidential election to the House of Representatives, under the provision of the 12th Amendment of the Constitution. This scenario played out in 1824, when Andrew Jackson won a plurality of electoral and popular votes but was defeated in the House by John Quincy Adams.

Whether wealthy donors would fund a candidate with such long odds is unclear. Dan Senor, a former Romney adviser and a confidant of House Speaker Paul D. Ryan (R-Wis.), has been informally briefing high-level GOP donors opposed to Trump on how an independent campaign might work and has found them to be willing to invest if the right candidate stepped forward, according to people involved.

Spencer Zwick, who was Romney’s 2012 national finance chairman, said: “If this was just a ‘Never Trump’ option and there’s no hope of actually winning — in other words, a kamikaze mission — I’m not sure there’s enough money. If there were a real alternative, it changes­ the dynamic. But who’s going to do that?”

An obvious possible contestant is Kasich, who portrayed himself in the GOP primaries as a pragmatist with crossover appeal. Since he dropped out, Romney and other Republicans have tried to persuade him to forge an independent run.

But Kasich’s advisers dismissed the idea. “The governor is not entertaining nor will he run as an independent,” spokesman Chris Schrimpf said.

John Weaver, Kasich’s chief strategist, said of the governor’s courters: “They had plenty of time and opportunity to influence the [GOP] nomination battle in a constructive way, and they didn’t for whatever reason. The idea of running someone as a third party, particularly the way they’re going about it, is not going to be effective and is not practical.”

A Romney representative declined to comment. The former nominee has been stinging in his public critiques of Trump, and, in a Facebook post on Wednesday, he tried to shame the business mogul into releasing his tax returns.

Romney also has communicated with Sasse, 44, who has become a favorite of elite conservatives since joining the Senate last year. Sasse spokesman James Wegmann declined to comment on Sasse’s private conversations.

As an ardent defender of conservatism, Sasse is seen by some party leaders as a future national candidate. He stirred a political storm by declaring on social media that he could not support Trump and wanted “some third candidate — a conservative option, a Constitutionalist.”

But any hunger for Sasse as that candidate seems limited. Fans launched an unofficial “Draft Sasse” committee May 4, but a week later, it counted less than 700 followers on Twitter and 49 on Facebook.

Publicly, Sasse has also repeatedly ruled out the idea of running — “The answer is no,” Wegmann reiterated — but Republicans who have discussed the possibility with him think he has not closed the door entirely.

Nor is Sasse shying away from the attention. He will deliver a keynote speech Monday on economic opportunity at the American Enterprise Institute, a conservative think tank in Washington. Speaking out about Trump could position him favorably in a field of ambitious rivals should Trump lose in November and as the GOP searches for new stars to help it rebuild.

One of Sasse’s boosters is Stevens, Romney’s former chief strategist. As with many people discussing an independent effort, Stevens sees Sasse as an optimist who could be the ideal antidote to the deeply polarizing Trump and Clinton.

“I’ve never met Ben Sasse, and I don’t have a connection with him, but I’m really moved by what he says,” Stevens said. “He has a wonderful tone, and he’s exactly right. . . . If Ben Sasse ran, I’d guarantee that he’d have higher favorability at the end than any other national politician.”

The third-party plotters represent only a sliver of what in the primaries became known as the “Never Trump” movement. Many Republicans opposed to him — from former Texas governor Rick Perry to Sen. Marco Rubio (Fla.) — now are lining up behind the presumptive nominee, if not always enthusiastically.

“You’re talking about a very shallow group,” said Ed Cox, chairman of the New York Republican Party and a Trump supporter. He criticized most of the organizers as conservatives who care more about “their own intellectual constructs” than the “voice of the people.”

Two central figures in the draft talks are Kristol, who edits the Weekly Standard, and Erickson, a talk-radio host. While Kristol acts as a lone operator and has huddled privately with Romney and other Republicans, Erickson leads an organized group with former Senate staffer Bill Wichterman and others called Conservatives Against Trump, which has been meeting regularly for months.

Coburn, known for his fiscal conservatism, and Sasse have been atop the group’s recruit list for some time. Wichterman is among those who have reached out to Coburn. Friends of the 68-year-old former senator said he is listening but is unlikely to pull the trigger, in part because of health concerns.

Earlier this spring, Kristol had his eyes on Mattis, who is revered by conservatives for his public break with the Obama administration. The general, now a fellow at Stanford University’s Hoover Institution, met for several hours in mid-April with Kristol, Wilson and GOP consultant Joel Searby at the Beacon Hotel in Washington to go over how a campaign could work.

But soon after, Mattis backed away from the idea because he wasn’t ready to risk politicizing his reputation with a campaign that had little hope for success, according to two people familiar with his deliberations who spoke on the condition of anonymity to discuss those conversations. Through a spokesman, Mattis declined to be interviewed.

Kristol then reached out to Romney, asking for a meeting to request his assistance. The two met May 5 at the J.W. Marriott hotel in Washington, where they talked about possible contenders. Kristol detailed their discussion the next day to The Washington Post, which irked some Romney associates.

When asked this week to comment on further developments, Kristol declined.

“These conspiracies for the public good are time and labor intensive!” he wrote in an email. “In any case, things are at a delicate stage now, so I really should keep mum. Suffice it to say that serious discussions and real planning are ongoing.”

One option off the table is McChrystal.

“I’m not entertaining any candidacy,” the former U.S. commander in Afghanistan wrote in an email. But, he added, “certainly a curious political campaign.”