Donald Trump and Hillary Clinton triumphed Tuesday in Florida's presidential primaries, capturing the biggest prize on a crucial day of voting and showcasing the strength of the two front-runners. Mr. Trump's victory was a devastating blow to Marco Rubio, all but ending the Florida senator's White House campaign.
Votes were being counted in Ohio, North Carolina, Missouri, and Illinois, but all were too close to call as polls closed.
Republicans were keeping an especially close eye on Ohio, where Trump was locked in a close race with the state's governor, John Kasich. A victory for the billionaire businessman in Ohio could put him on the clear pathway to the GOP nomination, with few opportunities for his remaining rivals to stop his stunning rise.
In Florida's winner-take-all Republican primary, he won 99 delegates.
Ms. Clinton, too, was looking to pull away from rival Bernie Sanders in Tuesday's contests. While Clinton holds a comfortable lead in the delegate count, Senator Sanders was eager for a burst of momentum from Ohio that could build on his surprising win last week in Michigan.
Reprising a theme that helped propel that victory, Sanders has pounded Clinton's past support for trade deals such as the North American Free Trade Agreement, which he says has been a job-killer in the US.
"When it came down whether you stand with corporate America, the people who wrote these agreements, or whether you stand with the working people of this country, I proudly stood with the workers," Sanders said during a campaign stop Tuesday in Ohio. "Secretary Clinton stood with the big money interests."
According to early exit polls, Democratic voters were more likely to describe Sanders as honest, but more likely to describe Clinton's policies as realistic.
Campaigning Tuesday in North Carolina, Clinton said "the numbers are adding up in my favor." She signaled an eagerness to move on to a possible general election showdown with Trump, saying he's laid out a "really dangerous path" for the country.
Trump entered Tuesday's primaries embroiled in one of the biggest controversies of his contentious campaign. The GOP front-runner has encouraged supporters to confront protesters at his events and is now facing accusations of encouraging violence after skirmishes at a rally last week in Chicago.
The vibe at Trump's events has deepened the concern over his candidacy in some Republican circles. Senator Rubio and Governor Kasich have suggested they might not be able to support Trump if he's the nominee, an extraordinary stance for intraparty rivals.
Trump's closest competition so far has come from Texas Sen. Ted Cruz, who is keeping close to the businessman in the delegate count. Senator Cruz has been urging Rubio and Kasich to step aside and let him get into a one-on-one race.
Even before Tuesday's results, however, a group of conservatives was planning a meeting to discuss options for stopping Trump, including at a contested convention or by rallying around a third-party candidate. While such no candidate has been identified, the participants in Tuesday's meeting planned to discuss ballot access issues, including using an existing third party as a vehicle or securing signatures for an independent bid.
A person familiar with the planning confirmed the meeting on the condition of anonymity because they were not authorized to discuss the gathering by name.
If Trump sweeps Tuesday's contests, he'll cross an important threshold with more than 50 percent of the delegates awarded so far.
Despite concerns from party leaders, Republican voters continue to back Trump's most controversial proposals, with two-thirds of those who participated in GOP primaries Tuesday saying they support temporarily banning Muslims from the United States.
The exit polls were conducted by Edison Research for The Associated Press and television networks.
Trump won easily in the Northern Mariana caucus on Tuesday, picking up nine delegates. That gave him 469 to 370 for Texas Sen. Ted Cruz, 163 for Rubio and 63 for Kasich. It takes 1,237 to win the GOP nomination.
Entering Tuesday, Clinton had 768 pledged delegates compared to 554 for Sanders, according to an analysis by The Associated Press. Overall, Clinton holds 1,235 total delegates, more than half the number needed to clinch the nomination when the count includes superdelegates, who are elected officials and party leaders free to support the candidate of their choice. Sanders has 580 when the count includes superdelegates.
Pace reported from Washington. AP writers Scott Bauer in Rockford, Illinois, Lisa Lerer in Chicago, Sergio Bustos in Miami, Stephen Ohlemacher and Alan Fram in Washington contributed to this report.