Where will Rubio voters go?
And the status of his delegates could become another thorny issue for the fraying Republican Party.
Republican Party rules require delegates to vote for their chosen candidate on at least the first ballot. But delegates' votes are also governed by state and local party rules, some of which prevent delegates from voting for another candidate even on a second or third ballot.
"While we are on the right side, this year we will not be on the winning side," Rubio said in his concession. But his pledged delegates, and his remaining supporters in states that have not yet held their primaries, could still give him some pull in the nominating process.
Republican Party of Virginia spokesman David D'Onofrio told AMI Newswire the specific rules on how delegates can vote, even if their candidate has quit the presidential race, is decided "state by state."
"In Virginia," D'Onofrio said, "delegates are bound through the first ballot." The 16 delegates Rubio won in Virginia's March 1 primary, he said, "remain with him."
Whether and how delegates are bound may be an academic exercise. Under the Republican Party's controversial "Rule 40," only those candidates who have won eight or more states will have their delegates counted in the first round of balloting.
Rubio, who won Minnesota, Puerto Rico, and the District of Columbia, did not clear that threshold. Only front-runner Donald Trump, who has won 19 contests, and Texas Sen. Ted Cruz, who has won nine, meet the Rule 40 standard for having their delegates counted on the first ballot.
Yet, with more delegates in his corner than Ohio Gov. John Kasich - who won his first, and so far only, race by taking the Buckeye State Tuesday night - Rubio may have room to make a deal.
Syndicated radio talk show host Tim Donner, who ran for a U.S. Senate seat from Virginia in 2012, told AMI Newswire that Rubio has three possible scenarios before him.
"Donald Trump may approach Rubio to be on his ticket in November," he said. "That may be a bridge too far, given all they've said to each other in the campaign, but it would allow Trump to put the race away."
Donner also suggested that Cruz might make a similar offer to Rubio. "Cruz would be wise to consider the same thing," Donner said. "It might get the establishment behind him, and it may answer a question that's hung over the whole campaign: Is the establishment's hatred of Trump greater than their fear of Cruz?"
Donner suggests a third Rubio option: to keep his delegates close, help deny Trump the nomination, and seek concessions from the leading candidate at the time. "Maybe he asks for a prime speaking slot at the convention," Donner said, "or perhaps a cabinet position."
Rubio supporters in Virginia are still mulling what to do after Tuesday night's announcement.
Senior Republican strategist Shaun Kenney told AMI Newswire that he believes Rubio supporters in the upcoming primary states will likely split their support between Cruz and Kasich.
But, "Trump is mathematically so far ahead, even a concerted effort to defeat him is an uphill struggle," he said.
Delegate Tim Hugo (R-Chantilly), who chaired Rubio's campaign effort in Virginia, told AMI Newswire he doesn't know what will happen to Rubio's delegates or his supporters in other states, but said he will "strongly and enthusiastically support our Republican presidential nominee."