Donald Trump calls for Republican unity behind his presidential bid

Hours after claiming three more victories, Republican presidential front-runner Donald Trump called on his party's mainstream wing to stop resisting his candidacy as his White House rivals embarked upon a weeklong march to block the billionaire businessman from building an insurmountable delegate lead.

"Instead of fighting it, they should embrace it," Trump said in a Wednesday interview with Fox News Channel. "If we embrace what's happening and if everybody came together ... nobody could beat the Republican Party."

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Trump's easy victories the day before in Michigan, Mississippi and Hawaii left his opponents with shrinking opportunities to slow his momentum in the Republican primaries and little indication that intense efforts to undermine his credibility are pushing voters away from the brash billionaire.

Clinton pads lead

On the Democratic side, Bernie Sanders surprised front-runner Hillary Clinton on Tuesday in Michigan, a victory that breathed new life into his White House bid and forecast a long Democratic contest. But Clinton, who won Mississippi, padded her delegate lead and is now halfway to the number needed to clinch the nomination.

Clinton glossed over her contest with Sanders as she addressed supporters, choosing instead to focus her attention on Republicans and the general election.

"We are better than what we are being offered by the Republicans," she declared.

5 states vote Tuesday

The fight to stop Trump now shifts to five states that will vote next Tuesday none bigger than Florida and Ohio, winner-take-all contests that could destroy or resurrect the chances of home-state candidates Florida SenatorMarco Rubio and Ohio Gov. John Kasich.

His closest rival, Texas SenatorTed Cruz, received a boost Wednesday with an endorsement from former GOP rival Carly Fiorina, who despite her failed campaign, could prove to be an asset with donors.

Rubio, meanwhile, suffered another brutal drubbing Tuesday night, failing to pick up any delegates in Michigan and Mississippi and finishing a distant third in Hawaii and Idaho. Similarly, Ohio Gov. John Kasich finished no better than third place in the four primary contests.

"He's not going to win in Ohio. We're going to win in Ohio," Kasich said Wednesday of Trump on ABC's "Good Morning America." "That's going to be a whole new ball game and we'll be moving all across the Midwest."

With a Tuesday night win in Idaho, Cruz hopes to play spoiler in the next round of contests, bolstering his case that he's the only candidate who can beat Trump with some regularity.

Attacks fail to slow Trump

With the prospect of a Trump nomination growing more likely, rival campaigns and outside groups have significantly stepped up efforts to discredit the real estate mogul. But the flood of attacks on Trump's business record and temperament has failed to slow his rise.

"Every single person who has attacked me has gone down," Trump said at one of his Florida resorts. He was flanked by tables packed with his retail products, including steaks, bottled water and wine, and defended his business record more thoroughly than he outlined his policy proposals for the country.

He told NBC's Todayshow Wednesday he thought the attacks were helping him: "There's tremendous positive energy in the party. We're setting records going to the polls. Some people have never voted before and they've voting for Trump."

Tuesday's contests marked another lost opportunity for rivals desperate to stop his march to the nomination. Next week's winner-take-all contests in Ohio and Florida loom as perhaps the last chance to block him short of a contested convention fight.

As Kasich expressed optimism about Ohio, Rubio, whose appeal with party leaders hasn't been reciprocated by voters, insisted he would press on to Florida.

"It has to happen here, and it has to happen now," Rubio told supporters Tuesday at a Sarasota rally.

Ohio, Florida are key primaries

If Rubio and Kasich can't win at home, the GOP primary appears set to become a two-person race between Trump and Cruz. The Texas senator is sticking close in the delegate count, and with seven states in his win column he's argued he's the only candidate standing between Trump and the GOP nomination.

Trump won most of the delegates in Tuesday's contests but he still must do better to win the nomination before the Republican 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. Marco Rubio has 151 delegates and John 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.