With Rubio's decision to drop out, three Republican candidates remain in the White House race Trump, Kasich and Cruz.
Veiled rebuke of Trump's campaign tactics, Rubio warned that the politics of division will leave America a "fractured nation." "America is in the middle of a real political storm, a real tsunami and we should have seen this coming," Rubio said. "While we are on the right side," he said, "this year, we will not be on the winning side."
Rubio spent the final weeks of his campaign in an often bitter fight with Trump.
Former presidential candidate Marco Rubio told supporters to Texas Senator Ted Cruz is now "the only conservative left in the race" but he said he has no interest in running as Cruz's vice president, or anyone else's for that matter.
Cruz also praised Rubio warmly, saying he could "paint a picture and weave a tapestry about the promise of America like nobody else." And Cruz told Rubio's bereft supporters: "We welcome you with open arms."
Rubio praised Cruz's conservative credentials and said he chose not to take his campaign all the way to the convention because winning in a contested convention "would be pretty much fatal for the party."
He said that now that he is dropped out of the presidential race and the GOP field has "narrowed," he was hopeful Republicans could coalesce around an alternative to GOP frontrunner Donald Trump.
"Hopefully there is still time to prevent a Donald Trump nomination, which would fracture the party and be damaging," Rubio said.
But he offered no clarity on his own political future, telling reporters only he planned to leave politics for a time after his current term in the Senate is done.
"I'm going to finish my term here in Senate, work hard and then be private citizen in January," he said.