Alarmed by Donald J. Trump's victories in seven states on Super Tuesday, Republicans desperate to sink his presidential bid moved Wednesday to battle him on two fronts, attacking him with millions of dollars in television ads in Florida while girding for what would be the party's first contested convention in 40 years.
The urgent new efforts, led by a group of corporate executives, financiers and Republican strategists, came as more party leaders expressed fear that Trump's nomination would taint the party with a stigma of bigotry and recklessness. Yet many also acknowledged that it was now all but impossible to defeat Trump outright during the primary season.
Still, the focus on Florida, which holds its primary on March 15 — and where many of the anti-Trump forces also hope to see Sen. Marco Rubio prevail, so he can continue in the presidential race — prompted fresh contributions to groups planning sustained attacks on Trump. In short order, three groups reserved $5 million of airtime in the state, a figure that is likely to grow.
In a preview aimed at sobering Republican voters, one of the groups, Our Principles PAC, released a Web ad called "Unelectable," presenting what it warned would be "coming this fall from the Democratic Party" if Trump was nominated: clips of journalists and entertainers seizing on a variety of Trump's statements as racist, of white supremacist David Duke expressing support for Trump, and of Trump refusing to condemn Duke.
But stopping Trump in Florida and in Ohio, which also votes on March 15 and where Gov. John Kasich hopes to carry his home state, would be only the first step in an increasingly unlikely plan to block Trump from the Republican nomination.
Veteran Republican officials and aides to Trump's rivals say they are now focused above all on denying him the 1,237 delegates he would need to clinch the nomination before the party gathers in Cleveland in July.
"Trump is on track to have such a dominating lead in the number of delegates, and with that big of a lead it's going to be hard to catch him before the convention," said Benjamin Ginsberg, a Republican campaign lawyer and rules expert.
That would give rise to the first convention since 1976 in which Republicans convened without already having settled on their nominee. And given the growing number of Republicans who have ruled out supporting Trump if he becomes the party's standard-bearer, the convention could become the kind of defining, which-side-are-you-on moment that scars the party, or worse, splits it in a fashion not seen since Theodore Roosevelt abandoned it in 1912.
Much of the immediate challenge for those opposed to Trump is that there is no consensus about who is the best alternative to him. After Sen. Ted Cruz of Texas won three states on Tuesday, his aides said he would make his case by letting his success do the talking.
Jeff Roe, his campaign manager, said: "Just win."
Cruz, who is hoping for victories in a group of contests on Saturday in which only registered Republicans may vote, caught a break on Wednesday when Ben Carson, the retired neurosurgeon, said that he saw no path forward for his campaign.
Cruz's aides believe Carson's evangelical supporters will flock to Cruz.
But Rubio, who won only Minnesota, and Kasich, who carried no states, showed no sign of yielding.
In fact, Rubio's allies in Washington have asked lawmakers who have endorsed his campaign to reach out to Cruz and to Kasich to urge them to withdraw, according to people briefed on the Rubio campaign's efforts.
But repeated attempts to clear a path for Rubio have failed, and the Super Tuesday elections have only complicated matters for him, since Cruz fared significantly better than he did.
Kasich, on the campaign trail in Michigan, looked forward to the March 15 contests as clarifying.
"Look, it gets down to, can he win Florida?" Kasich said of Rubio. "Do I win Ohio? And that's what we'll see. Because if you can't win your own state, then I don't know how you move on."
If Trump's momentum is enough to carry him to victory in Ohio and Florida, which both distribute their delegates on a winner-take-all basis, the Republican race may effectively be over. He will have dealt Rubio and Kasich humiliating losses in their home states and netted 165 delegates, putting him on course to capture a majority before the convention.
But the converse is also true, said Rick Hohlt, a longtime Washington Republican deeply engaged in the delegate-counting process. "There's a general agreement that it's mathematically very difficult for Trump to get the nomination with delegates before the convention if he is beaten in those two states."
Of the Stop Trump effort, Hohlt added: "Florida and Ohio are the linchpin."
More immediately, the anti-Trump forces — primarily wealthy donors and corporate executives closely aligned with senior party leaders — are mobilizing in Florida. Polls have indicated Trump enjoys a lead there, early votes are already being cast, and there is still a lingering — if dimming — hope that Rubio is the Republican most capable of defeating Trump in a one-on-one contest.
In what will be the first well-financed ad assault Trump has faced since the final week before the Iowa caucuses, the anti-tax Club for Growth has reserved $1.5 million in cable television time in Florida, the conservative America Future Fund has reserved $1.75 million in broadcast time and the super PAC supporting Rubio, Conservative Solutions, has laid down another $1.75 million.
Our Principles PAC, which is devoted solely to defeating Trump, is also expected to begin running ads in Florida. All told, the anti-Trump groups are likely to spend more than $7 million in the state.
"This is yet another desperate attempt by the out-of-touch establishment elites and dark money, that control the weak politicians, to maintain control of our broken and corrupt system," said Hope Hicks, a spokeswoman for Trump's campaign.
On a conference call with donors on Tuesday evening, three leaders of the effort to stop Trump pleaded for support: Meg Whitman, chief executive of Hewlett-Packard; Todd Ricketts, a co-owner of the Chicago Cubs; and Paul Singer, a hedge-fund billionaire. In particular, they urged about 50 participants in the call to fund Our Principles PAC.
The call was led by Brian Baker, an adviser to the Ricketts family, who warned that it would be difficult to stop Trump but that, for the sake of the party, they had to try, and that this was the crucial moment to slow his march to the nomination, according to participants in the call.
Stopping Trump in Florida or Ohio makes it at least possible to hold him short of a delegate majority before the convention. Two other factors offer his opponents hope: Many of the remaining state contests will be closed primaries, in which only Republicans can vote; Trump has drawn heavily from independents when they are able to cast ballots. And all but six states voting after March 15 will award delegates proportionally.
A contested convention would bring into play a series of complicated and crucial procedural votes. Perhaps the most significant would address a current rule stating that no candidate can be placed in nomination without having won a majority of delegates in eight states.
"The best case scenario for the Never Trump backers is to throw the convention into disarray, either by ensuring Trump does not reach the eight-state threshold so the rules have to be changed, or by changing the rules even if he does," said Jeff Berkowitz, a former Republican National Committee official.
But if Trump is able to clear the eight-state bar, his supporters will aggressively resist any effort to revisit it.
To actually defeat Trump at the convention, Republicans would have to hope that he is first unable to win a majority on the initial floor vote. He would then have to be thwarted on subsequent ballots by delegates who abandon him and choose an alternative whose name has been placed in nomination. Rules vary state by state, but most delegates who are bound on the first ballot by how their states voted are free to support any candidate in later balloting.
Preparing for this possibility, Trump and some of his rivals have already begun the painstaking process of trying to elect friendly delegates in case those individuals become free agents on subsequent ballots.
But many veteran Republicans admitted that getting all the pieces to fall into place to defeat Trump would require the political equivalent of drawing an inside straight.
"I think it will be very difficult for anybody to keep him from getting the nomination now," said Jim Nicholson, a former Republican national chairman. "He has so much momentum."