Former Republican presidential candidate Sen. Marco Rubio said Sunday that he fully supports former rival Donald Trump’s White House bid, apologized for his personal attacks in the bruising primary and hinting that he’d even speak for Trump at the July nominating convention.

“I want to be helpful,” the Florida senator said on CNN's "State of the Union."

Rubio argued that supporting Trump, now the presumptive GOP presidential nominee, is the only way to keep Democratic front-runner Hillary Clinton from becoming president, regardless of some of his scorched-earth campaign rhetoric.

“Despite all my differences with Donald Trump, I have a better chance to get a conservative-nominated Supreme Court with him than I ever will with Hillary Clinton,” he said.

Rubio said Trump also will support other parts of the conservative agenda including the repeal of ObamaCare and rolling back federal regulations that are “damaging” to the U.S. economy.

Rubio suggested early last week that he wanted to help Trump defeat Clinton but that his decision was difficult.

Trump, through the primary season, which concludes June 7, repeatedly attacked Rubio, calling him “Little Marco” and suggesting his response to a debate attack in New Hampshire by New Jersey Gov. Chris Christie was a “meltdown” and robotic.

With his campaign failing, Rubio later went on the counter-attack, challenging Trump’s manliness by saying he had “tiny hands.”

On Sunday, Rubio said he privately apologized to Trump for the remark.

Rubio also suggested no single mistake led to his failed campaign, which he ended in mid-March after losing his home-state primary. But he suggested the personal attacks on Trump and not attacking Christie’s record in the debate were significant.

“If I had to do it over again, I just would have gone after him and attacked his record,” Rubio said.

Rubio, who is not seeking re-election in November for his Senate seat, was non-committal about his political future, saying again only that he might have sought re-election had friend and Lt. Gov. Carlos Lopez-Cantera not entered the race.