Sen. Marco Rubio (Fla.) won’t say whether he would accept a place on the national GOP ticket, but he’s already assumed the attack-dog-in-chief mantle, the quintessential role of a modern vice presidential nominee.

Rubio used searing rhetoric today to dig into President Barack Obama and his administration, charging that the one-term-Senator-turned-president has been in Washington, D.C., too long and “has lost himself.”

He argued that Obama has divided — and not united — the country, striking at the core message of the president’s 2008 campaign.

“He’s running dividing Americans against each other — obviously because he can’t run on his record,” Rubio said on “Fox News Sunday.”

In particular, he criticized Obama’s handling of the assassination of Osama bin Laden.

“He has taken something that should unite the American people … and turned it into a weapon for political warfare,” Rubio said.

“One of the reasons why he won was because he told the American people he knew how to fix it,” the Florida lawmaker said.” “[But] things have not gotten better. His party ran two chambers of Congress and he could have gotten anything he wanted and he got health care and the stimulus.”

Rubio also criticized the foreign policy credentials of Vice President Joseph Biden.

“Joe Biden’s record on foreign policy is one of being wrong on almost everything he’s ever advised or everything he’s ever asked for,” Rubio said, pointing to Biden’s plan as a Senator to decentralize Iraq into different regions and his admission that he advised the president against the raid that killed bin Laden. “That being said, I think he’s a very nice person.”

Biden was chairman of the Senate Foreign Relations Committee when he served in that chamber, and Rubio is now a member of that committee.

Rubio, of course, is leading in the Beltway speculation poll on whom presumptive Republican presidential nominee Mitt Romney will select as a running mate. It’s widely believed Rubio, who is of Cuban heritage, could help Romney with the Latino vote.

Romney has said the election likely will hinge on being able to mobilize Hispanic voters.

At a private fundraiser last month, the former Massachusetts governor told a group of donors: “We have to get Hispanic voters to vote for our party,” adding that Obama winning the voting bloc handily “spells doom for us.”

Rubio was so on-message on this morning’s talk show that host Chris Wallace cracked a smile when Rubio answered a question about his own relative inexperience by hammering the president on being in Washington too long and falling victim to the “point of diminishing returns in Washington” where lawmakers become “divisive, cynical, given to hyperbole on these issues.”

The former Speaker of the Florida state House declined to answer Wallace’s repeated attempts to get him to answer the will-you-or-won’t-you vice president speculation questions.

“I’m not going to talk about the vice presidential process. But I can tell you there are multiple ways someone can help our nominee, and I look forward to doing that,” Rubio said. “I hope I did that today.”