Trump expressed his support on Twitter yesterday, saying: “Poll data shows that @marcorubio does by far the best in holding onto his Senate seat in Florida. Important to keep the MAJORITY. Run Marco!"
However, the junior senator from Florida has said repeatedly he has no plans on running for re-election.
Trump’s support came just hours after Rubio announced he would attend the GOP convention in July. Rubio told CNN's Jake Tapper that he would release his 165 delegates to vote for Trump at the convention.
The Florida senator, who was once part of the #NeverTrump movement, has still not formally endorsed Trump, but insists he would “honored” to help defeat Clinton.
“I don't want Hillary Clinton to be president. If there's something I can do to help that from happening, and it's helpful to the cause, I'd most certainly be honored to be considered for that,” Rubio said.
Rubio took to Twitter today to say he will not be voting for Clinton in November.
With less than a month left to meet the filing deadline, Rubio expressed uncertainty after he leaves the Senate in January 2017, and did not shut down the possibility of returning to elected office.
"I can tell you I enjoy public service. If there's an opportunity to serve again in a way that I feel passionate about, I'll most certainly think I would explore it," Rubio said. "But I don't know where I'm going to be in two years. I don't know what my life will look like then."
Republicans are deeply concerned about losing Rubio's Senate seat to a Democrat.
Republican officials expressed confidence in the field of five GOP candidates to replace Rubio in Florida, though none have emerged as a clear favorite in the August primary.
"Sen. Rubio has always – has done a great job for Florida," a National Republican Senatorial Committee (NRSC) official said, adding "I think he’s focused on a lot of other things. But he’s been nothing but helpful to the committee since his presidential race ended and he did an event just last week."
ABC’s Benjamin Siegel and Ali Weinberg contributed to this report.