Romney begins search for a popular running mate to beat Obama Religion is also an underlying factor, with Mr Romney, a Mormon, performing consistently badly with evangelical Christians and Tea Party activists who supported the evangelical Catholic Rick Santorum until he dropped out of the race last week. Early choices for running mate appeared to be between charismatic performers - such as Chris Christie, the Catholic governor of New Jersey, or the Catholic Florida Senator and Tea Party darling, Marco Rubio - who could both fill the gap left by Mr Romney's inability enthuse the voters, and a safer pair of hands that would not upstage him. Among the leading candidates in the safe category is Rob Portman, a virtually unknown senator from the swing state of Ohio, who is said to have a close personal rapport with Mr Romney and would definitely not upstage him during the campaign. Analysts say that a myriad of considerations go into the calculation: can they deliver a swing state or demographic? Are they ready to be a heartbeat away from the presidency? Can they forge a working relationship with the nominee? "Personal chemistry is a critically important - but who is picked depends on how Governor Romney balances all the competing criteria," said Whit Ayres, an independent Republican pollster. Rob Portman is a very, very gifted man who really understands politics and puts a finger on the scale for Ohio; Marco Rubio [a Hispanic from the swing state of Florida] is charismatic and obviously interesting for other reasons. Conservative commentators have raised concerns that Mr Romney, who has failed to fire up the Republican base, might go for the safe choice and put personal and egotistical considerations over national ones. Jeffrey Lord, a former Reagan aide and Republican party historian, recalled George Bush Snr's decision in 1988 to pick the then little-known figure of Dan Quayle over Congressman Jack Kemp, a hugely charismatic former American football quarter back. Romney should not be afraid to pick someone who is his equal. Strong vice-presidential candidates - like Biden for Obama, Gore for Clinton, Lyndon Johnson for Kennedy or Bush for Reagan - say 'I want someone who is just as experienced as I am and is not my junior partner,'" Mr Lord said. There are people who have star power on their own - like Christie and Rubio - and Romney should not shy away from them, particularly because of his own weaknesses. If this evolves into a personality thing, and it's all about loyalty to Mitt Romney, that's not good. If this is about picking the best person, who's got some sparkle and experience and if Romney doesn't care if everyone adores his Vice President, that's a good thing. What seems certain following the appointment of Ms Meyers is that Mr Romney will not, like the McCain campaign in 2008 when they appointed Mrs Palin, be taking any snap decisions, with the New York Times predicting the vetting process this time around would be akin to a "body cavity search." "She knows Mitt's personal management style better than anyone," said Eric Fehrnstrom, another of Mr Romney's trusted advisers of Ms Meyers, "she knows how he operates, that he welcomes debate and discussion, that he works best with data."