Mitt Romney is spearheading an effort to find a third-party candidate to stop presumptive Republican presidential nominee Donald Trump.Other key operatives in the movement,reports, are William Kristol, editor of The Weekly Standard; Erick Erickson, RedState.com editor — along with strategists Mike Murphy, Stuart Stevens and Rick Wilson."These conspiracies for the public good are time and labor intensive!" Kristol told the Post in an email when questioned about the effort. "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."A representative for Romney declined to comment to the Post. The former Massachusetts governor, who lost the 2012 race to President Barack Obama, attacked Trump this week for failing to release his tax returns.While some Republican insiders have admitted that such an effort could be futile, the group has several targets, the Post reports.They include first-term Nebraska Republican Sen. Ben Sasse, who is among Trump's harshest critics, and Ohio Gov. John Kasich, who withdrew from the 2016 sweepstakes on May 4.Romney has reached out to both in recent days, according to the report.They've even reached out to Dallas Mavericks basketball team owner"I don’t see it happening," Cuban told the Post in an email."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."As for Kasich, "the governor is not entertaining nor will he run as an independent," spokesman Chris Schrimpf said.John Weaver, Kasich’s chief strategist, further told the Post: "They had plenty of time and opportunity to influence the 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."Regarding Sasse, 44, Romney has also talked with him, the Post reports. James Wegmann, the senator's spokesman, declined to comment on Sasse's private conversations.Though the senator has publicly ruled out a run — "The answer is no," Wegmann told the Post — Sasse is speaking to the conservative American Enterprise Institute think tank in Washington on Monday.His speech will be on economic opportunity, the Post reports."I’ve never met Ben Sasse, and I don’t have a connection with him, but I’m really moved by what he says," Stuart Stevens, who was Romney's chief strategist, told the newspaper. "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."