FORT MYERS, Fla. (AP) -- His party in disarray, a surging Donald Trump called on mainstream Republicans to unify behind his candidacy on Wednesday as his White House rivals pursued their last best opportunity to block the billionaire businessman from building an insurmountable delegate lead in two key states.
The often-brash Trump softened his tone, at least temporarily, hours after securing three more primary victories, praising House Speaker Paul Ryan as a man he respects and encouraging Mitt Romney to promote party harmony. As for his own campaign, he said he's poised to score a knockout in next week's winner-take-all primaries in Florida and Ohio.
"If I win those two, I think it's over," he told CNN's "Anderson Cooper's 360."
"Instead of fighting it, they should embrace it," he added on Fox News Channel. "If we embrace what's happening and if everybody came together ... nobody could beat the Republican Party."
Still, amid growing resistance to Trump's insurgent campaign, a number of former GOP presidential hopefuls have re-emerged in support of his current rivals.
Former Florida Gov. Jeb Bush planned to confer with all the candidates — save Trump — ahead of Thursday's GOP debate. He was meeting privately with Florida Sen. Marco Rubio on Wednesday, and planned to meet with Texas Sen. Ted Cruz and Ohio Gov. John Kasich on Thursday, said Kristy Campbell, Bush's former campaign spokeswoman. She provided no details.
Bush and Trump engaged in heated confrontations throughout Bush's campaign, repeatedly referring to each other as a "loser."
Rubio took Bush's attacks a step further in recent weeks, poking fun at Trump's tan, hair and hand size. Now, in the midst of a weeklong march through Florida to save his candidacy, Rubio concedes he made a mistake.
"My kids were embarrassed by it and if I had it to do over again I wouldn't," he said on MSNBC Wednesday night.
Cruz intensified his own bid to blunt Trump's momentum with an endorsement from a former rival, retired business executive Carly Fiorina, who offers him an immediate dose of credibility with his party's skeptical donor class.
Acknowledging many mainstream Republicans fear Cruz is too conservative, Fiorina told a Miami crowd that she's "horrified" by Trump.
"The truth is that Donald Trump and Hillary Clinton are two sides of the same coin," she charged. "It is time now to unite behind the one man who can beat Donald Trump, who can beat Hillary Clinton."
As the competing calls for unity suggest, the Republican Party's 2016 contest is far from settled a week before the high-stakes contests in Florida and Ohio that could finish off home-state candidates Rubio and John Kasich or resurrect their anemic candidacies.
On the Democratic side, Bernie Sanders surprised front-runner Hillary Clinton with a win Tuesday night in Michigan, a victory that breathed new life into his White House bid and forecast a longer Democratic contest. But Clinton, who won Mississippi, padded her delegate lead and is now halfway to the number needed to clinch the nomination.
Tuesday's contests in Michigan, Mississippi, Idaho and Hawaii signaled bad news for Republican officials across the country who fear that both Trump and Cruz — the day's only GOP winners — are wholly unelectable in a general election.
"The Republican establishment is in its death throes," said longtime tea party leader Mark Meckler. "The only remaining candidates are 100 percent anti-establishment."
Trying to put the focus back on Clinton, the Republican National Committee on Wednesday filed a federal lawsuit against the Obama administration trying to force the release of additional communications between Clinton's State Department, her campaign and senior aides.
"If this administration claims to be the 'most transparent in history,' and Clinton the 'most transparent person in public life,' then they should prove it, release these records, and allow the American people to hold her accountable," RNC chairman Reince Priebus said.
Yet the 2016 political conversation still focused largely on Republican infighting as the fight to stop Trump shifted to five states that will vote next Tuesday — none bigger than Florida and Ohio.
Trump has won and 15 of 24 Republican nominating contests so far but he still must do better to win the nomination before the GOP's national convention this summer.
His lead over Cruz grew by only 15 delegates Tuesday. That's because all four states awarded delegates proportionally, so even the second-place finisher got some. In the overall race for delegates, Trump has 458 and Cruz has 359. Rubio has 151 delegates and Kasich has 54.
It takes 1,237 delegates to win the Republican nomination for president.
For Democrats, Clinton has accumulated 1,221 delegates and Sanders 571, including superdelegates. Democrats need 2,383 delegates to win the nomination.
The delegate math highlights the importance of primaries in states like Ohio and Florida, which allocate all of their delegates to the winner.