Sen. Marco RubioMarco Antonio RubioJeb Bush calls for Broward County official to be removed from post Florida Dem rep: Scott is 'spinning conspiracy theories' Gillum retracts concession in Florida governor's race MORE (R-Fla.), who has yet to endorse de facto GOP presidential nominee Donald TrumpDonald John TrumpDeath toll in Northern California wildfire rises to 48: authorities Graham backs bill to protect Mueller Denham loses GOP seat in California MORE, said Thursday he would be willing to speak for the businessman at the party's national convention in July. 

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"If Donald Trump asked you to speak on his behalf, you would do so?" CNN's Jake Tapper asked Rubio.

"Certainly, yeah. I want to be helpful," responded Rubio, who was one of Trump's most vocal critics during the Republican primary.

"I don't want to be harmful because I don't want Hillary ClintonHillary Diane Rodham ClintonOvernight Defense — Presented by Raytheon — First lady's office pushes for ouster of national security aide | Trump taps retired general as ambassador to Saudis | Mattis to visit border troops | Record number of female veterans to serve in Congress Election Countdown: Lawsuits fly in Florida recount fight | Nelson pushes to extend deadline | Judge says Georgia county violated Civil Rights Act | Biden, Sanders lead 2020 Dem field in poll | Bloomberg to decide on 2020 by February What midterm exit polls tell us about 2020 MORE to be president. My policy differences with Donald Trump — I've spent a lot of months talking about them, so I think they're understood." 

Rubio, who suspended his campaign in March after losing badly to Trump in his home state, has previously declined to explicitly support or endorse Trump, instead saying he will "support the nominee." 

But Rubio has changed his tune, saying he would be "honored" to help Trump, who reached the 1,237 delegates needed to secure the Republican nomination Thursday, according to The Associated Press.

"I most certainly would be honored to be considered for that," Rubio told Tapper.

When asked earlier this month whether he would speak on behalf of Trump's nomination, Rubio demurred

"Donald Trump would be best served by having people out there working for him that agree with his policies and are enthusiastic about this campaign and enthusiastically supporting the things he has stood for," Rubio told the "Today" show.

Rubio on Thursday did not address rumored “pressure” from the GOP to change his mind and run for reelection to the Senate this November, but he left the door open for seeking political office in the future.

"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."