At present, freshman Florida Republican Sen. Marco Rubio is thought to be a slight favorite to be Mitt Romney’s running mate in the upcoming presidential election. But according to Pat Buchanan, the former MSNBC contributor and author of “Suicide of a Superpower: Will America Survive to 2025?” that seems unlikely.

During his regular appearance on “The McLaughlin Group” this weekend, Buchanan gave his thoughts on a Rubio vice presidential candidacy.

“He is young, he is Hispanic, He is from Florida. He can probably bring Florida,” Buchanan observed. “He is conservative. He’s a very attractive candidate, John. But I don’t know he’s going to get it. I think he has created a problem for himself.”

That problem, he said, is a shift toward neoconservatism on foreign policy.

“He has moved with the neoconservatives,” Buchanan said. “At his speech over at the Brooking Institution, he not only, you know, said that Putin was basically a weak leader, he said we should get involved in Syria — and maybe, militarily, we’ll have to attack Iran. He’s with Joe Lieberman and [John] McCain and Lindsay Graham and that crowd. And I don’t think that’s a winner right now.”

Buchanan also said Rubio’s youthful appearance, compared with Romney, is a potential problem.

“And I also think when you saw them together, it looked like he was too young and I think too callow to be the vice president of the United States,” he continued. “I think Romney is going to go with someone who is perceived as heavier and older. And the primary consideration: Can he be president of the United States on a moment’s notice?”

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