Marco Rubio's presidential campaign hit its nadir on Tuesday night when the Florida lawmaker lost his home state's primary to Republican front-runner Donald Trump.
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.
Instead of hurting him, Trump's bombastic attitude helped him win the 99 delegates up for grabs in Florida.
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.
The vibe at Trump's events has deepened the concern over his candidacy in some Republican circles. Rubio and 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. 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.
On the Democratic side, former Secretary of State Hillary Clinton pulled away from rival Bernie Sanders with her win in Florida. While Clinton holds a comfortable lead in the delegate count, Sanders is 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 U.S.
"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.
Votes were being counted in Ohio, North Carolina, Missouri and Illinois, but all were too close to call as polls closed.
Based on reporting by The Associated Press.