Idaho billionaire Frank VanderSloot announced Wednesday he would back the freshman senator after his team determined in a 10-month evaluation that Rubio would both make the best President and be the most electable in a general election.
And he said in an interview that criticism of the 44-year-old Rubio's inexperience at the national level won't harm him.
"That is a valid question to ask, and yet we have a current President that was a freshman senator and ... we've seen that a freshman senator can get a lot of stuff done," VanderSloot told CNN. "It happens, in my opinion, to be all of the wrong stuff, but ... I believe that Obama has demonstrated that a young senator can get a lot of stuff done."
VanderSloot made the endorsement in a letter to top donors and the media, in which he laid out his thinking on each candidate that his team considered.
"In our opinion, Marco Rubio far exceeds the other candidates as meeting our requirements to be the best president, and he, importantly, is by far the most electable," VanderSloot wrote in his endorsement letter of Rubio.
He also took aim at other heavy-hitting Republican donors who aren't investing in the primary, calling it a "dangerous strategy" that could result in someone winning the primary who is "totally unelectable," slamming in particular Texas Sen. Ted Cruz and mogul Donald Trump.
VanderSloot is the founder of health products company Melaleuca and has been a substantial Republican donor in the past. He was a national finance co-chairman for Mitt Romney's 2008 and 2012 presidential campaigns, with his company donating more than $1 million to Romney's super PAC and with VanderSloot bundling $58 million for the 2012 campaign. He has also been a heavy donor to the U.S. Chamber of Commerce and leading conservative nonprofit groups Crossroads GPS and Americans for Prosperity.
Likes Rubio's immigration approach
In the interview, VanderSloot said Rubio is seen as the best chance to "unite" a country badly in need of it, that he has the right perspective on economic issues, knows his foreign policy and is strong on immigration.
"I believe that Marco Rubio has the right approach to immigration," VanderSloot said. "I know a lot of Hispanic people, I mean a lot of them ... I've talked to people and heard their stories, people who are not documented and what they're looking for, and honestly they love America."
"These folks aren't looking for citizenship, they're looking for a job," he added.
VanderSloot added that he hopes Rubio can bring Hispanic voters to the Republican Party, which should be attracted to the GOP's conservative values but turns off Latinos with many of the party's immigration policies.
The failed Romney campaign was often criticized for its position on immigration, with Romney's talk of self-deportation facing ridicule. At the time, even, VanderSloot said he wished Romney would be more like Rubio.
"I recall talking to Marco Rubio during the Mitt Romney campaign trying to get some of the folks at the Mitt Romney campaign to go more the direction of Marco Rubio," VanderSloot said. "I wasn't successful, but I tried."
VanderSloot pledged not just to support Rubio heavily from his own pocket, but to go "all out" in bundling money from other donors, as well. And he said he's heard from many friends who originally supported former Florida Gov. Jeb Bush that they like Rubio but are waiting until farther into the primary cycle to get involved.
He is just the latest major donor to sign on to Rubio's campaign, after billionaire Paul Singer and hedge fund manager Cliff Asness.
Rubio's last fundraising quarter was disappointing, but after strong debate performances, his rising poll numbers have placed him third in many surveys and big-money names have gravitated toward his campaign.
In his letter, VanderSloot said Carly Fiorina was his second choice for support, and that while many of his peers initially supported Bush, Rubio's one-time mentor, he has now become a "weaker" candidate.
"It has become increasingly clear that Jeb simply does not have the leadership skills necessary to unite the people behind him," he wrote.
VanderSloot also called Cruz and Trump unelectable and said Trump "would make a particularly poor president."
The Rubio campaign said it was "thrilled" to have VanderSloot aboard.
"Marco-mentum is building. Thrilled to have Idaho's Frank VanderSloot on @TeamMarco," Rubio's spokesman Alex Conant tweeted