Sen. Marco Rubio signs autographs during a meet and greet on Nov. 11 in Davenport, Iowa. (AP Photo/Charlie Neibergall)

Michigan businessman and prominent Republican financier John Rakolta Jr. endorsed Marco Rubio for president on Monday and has begun tapping his network of friends and associates to raise money for the Florida senator's campaign.

Rakolta, who served as a national finance co-chairman for Mitt Romney's 2008 and 2012 presidential campaigns and has been close to the Romney family for decades, is the latest top Romney ally to sign on with Rubio.

In a letter to friends, which he shared with The Washington Post, Rakolta writes, "America is facing new challenges that require new leadership. My entire life has been about looking forward not backward, and after carefully considering all the candidates for president, it's clear to me that Marco Rubio is best prepared to lead America forward in this new century."

Rakolta added, "Articulate and confident, he represents a new breed of Republican leader who can unite our party and win both the primary and general elections."

[Has the Marco Moment arrived?]

Rakolta, who is chief executive of Waldbridge and a major GOP money player in the Midwest, said he plans to host Rubio at a fundraiser in the Detroit area on Dec. 9. Rakolta joins fellow former Romney finance leaders Wayne Berman, Paul Singer and Frank VanderSloot on the Rubio campaign.

Rakolta said that he chose Rubio after weighing the candidacies of several other establishment favorites, including former Florida governor Jeb Bush, New Jersey Gov. Chris Christie and Ohio Gov. John Kasich.

[Mitt Romney warms to Marco Rubio as young senator cultivates relationship]

Although Romney has not endorsed in the 2016 race, he is said to have warmed to Rubio, and several of his former aides are now working for Rubio. Still, Rakolta said he made his decision independently. “I didn’t call Mitt," he said. "I didn’t ask Mitt for his blessing."

Rakolta said he met privately with Rubio in June at Romney's E2 Summit in Park City, Utah. "He listened very intently for a long period of time about what I have to say, which is very refreshing," Rakolta recalled.

Rakolta said he disagreed about Cuba policy with Rubio, a son of Cuban-American immigrants who is a staunch supporter of the Cuba embargo. A few months before their Utah meeting, Rakolta spent a week in Cuba, though Rakolta said they had a "very professional" discussion of their disagreements on U.S. policy with Cuba.

"It was done without name-calling and rancor," Rakolta said. "His whole style was engaging. He listened. He was intelligent....I understood his point of view. I found that very, very refreshing. It's the rare politician that will actually sit down and listen to you, look into your eyes and comprehend what you are saying."