Mitt Romney may be tight-lipped about his vice presidential short list, warning that only he and longtime aide Beth Myers know who is on it, but a close examination of the campaign’s activity suggests four contenders have risen through the ranks: Former Minnesota Gov. Tim Pawlenty, Ohio Sen. Rob Portman, Wisconsin Rep. Paul Ryan and Louisiana Gov. Bobby Jindal.

New Hampshire Sen. Kelly Ayotte and Virginia Gov. Bob McDonnell may be considered wild cards, and Romney has said he’s thoroughly vetting Florida Sen. Marco Rubio, though the first-term lawmaker’s status appears unchanged…

On readiness for office, conversations with Romney insiders and allies suggest that they have no qualms about Portman or Pawlenty. One of Romney’s biggest complaints about President Obama is that he is in over his head and had “never run anything before.” Pawlenty governed the state of Minnesota for two terms; Portman ran the Office of Management and Budget as well as the Office of the United States Trade Representative. Jindal is in his second term as governor of Louisiana. Paul Ryan, however, falls short in this regard; he was a Capitol Hill staffer and a marketing consultant before becoming a congressman at age 28.

As for chemistry with the candidate, Pawlenty, Portman and Ryan have all campaigned alongside him multiple times.