(CBS News) -- Now that Mitt Romney has become the presumptive nominee for the Republican nomination for president, all eyes in the political world are looking to see who he will pick to be his running mate. And a lot of Republicans are saying Florida Sen. Marco Rubio could be the number two on the Republican ticket this year.
But CBS News political director John Dickerson says Rubio does not have enough experience to pass what many see as the most important test for getting the nod: whether he can step in to be the president on a moment's notice.
"I think a fair reading of his career would suggest he doesn't" have the experience to step in and take over for Romney if something unexpected were to happen, Dickerson said on "CBS This Morning."
"Marco Rubio has no real executive experience. And that was one of the big knocks against candidate Obama (in 2008) and one of the reasons Republicans say the president has been a failure because he lacked that executive experience and that is a hurdle that Marco Rubio just can't clear right now," Dickerson said.
Dickerson noted that former Vice President Dick Cheney, who has often said the most important characteristic needed for a running mate is the ability to be president, was a surprise choice.
"Remember Dick Cheney was an out of nowhere pick for George W. Bush. He picked him because he said he had the kind of experience necessary to step into that job," Dickerson said, adding that "this pageant has a long way to go."
Dickerson said Romney and Rubio, who held a town hall together in Pennsylvania Monday, are out in public now because it is beneficial to both men.
The senator gets to increase his national profile and even if he does not end up on the ticket, Romney may pick up some votes in Rubio's Florida, which will be a crucial state in November.
"Rubio's Cuban heritage might help Hispanic voters be open to" Romney, Dickerson said, noting that it remains unclear what effect Rubio would have on Romney voters in other key states like Colorado and New Mexico.
To see the interview of Dickerson by "CBS This Morning" co-hosts Charlie Rose and Erica Hill, click on the video in the player above.