LANSING, Mich. — Donald Trump’s easy victories in Michigan, Mississippi and Hawaii left his rivals with shrinking opportunities to slow his momentum in the Republican primaries and little indication that a flurry of intense efforts to undermine his credibility are pushing voters away from the brash billionaire.

Democrat Bernie Sanders surprised front-runner Hillary Clinton 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.

Trump entered Tuesday’s contests facing questions about his durability and ended the night with a pair of convincing victories. Texas Sen. Ted Cruz added a win in Idaho, bolstering his case that he’s the only candidate who can beat Trump with some regularity.

Florida Sen. Marco Rubio suffered another brutal drubbing, failing to pick up any delegates in Michigan and Mississippi. He faces a sudden-death contest in Florida next week. Similarly, Ohio Gov. John Kasich desperately needs to win his home state Tuesday to stay in the race.

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.

While a handful of recent losses to Cruz have raised questions about Trump’s standing, 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.

Kasich finished third in Michigan, behind Trump and Cruz. It wasn’t the boost he was looking for heading into next week’s crucial contest in his home state.

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 at a Sarasota rally.

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.

During a campaign stop at a North Carolina church, Cruz took on Trump for asking rally attendees to pledge their allegiance to him. Cruz said the move struck him as “profoundly wrong” and was something “kings and queens demand” of their subjects.

Some mainstream Republicans have cast both Trump and Cruz as unelectable in a November faceoff with the Democratic nominee. But they’re quickly running out of options — and candidates —to prevent one of the men from becoming the GOP standard-bearer.