One name looms larger than all others as Mitt Romney prepares to select a Republican running mate, which his advisors now say could be as early as this week: Sarah Palin.
John McCain's fateful choice of the then-Alaska governor to round out the GOP ticket in 2008 broke the first rule of vice-presidential selection. He picked someone who would upstage him. It looked clever at first. But everyone knows how it turned out.
Not surprisingly, Mr. Romney is guided by a simple principle – do no harm – as he prepares to unveil his vice-presidential pick, which advisors have hinted might come as early as next week.
As a successful private-equity executive, Mr. Romney was known for making data-driven investment decisions, not gut choices. He is applying that discipline in making a VP pick. If his selection might still surprise pundits, it will not be because it is an impulsive one.
That has not stopped Republican commentators from offering unsolicited advice. Their dream VP pick is former Florida governor Jeb Bush. But most doubt Mr. Bush would be willing to play second fiddle to a candidate for whom he has shown little enthusiasm.
Hot shot New Jersey Governor Chris Christie is on many Republican wish lists, as is Florida Senator Marco Rubio, a gifted orator who might light a GOP fire among Latinos.
Vice-presidential nominees are usually named in late summer at the opening of party conventions. But Mr. Romney is considering unveiling his pick sooner to double up against President Barack Obama and Vice-President Joe Biden on the campaign trail.
As he pores over dizzying amounts of biographical detail, looking as much for red flags as for compelling personal narratives, Mr. Romney must weigh all of the obvious attributes: experience, intelligence, political acumen, swing state appeal, gender and race.
As a northeastern Republican known for moderation, he must also consider whether he needs a running mate with more conservative bona fides to win over the Tea Party. As a Mormon, he must decide if he needs a devout Christian at his side to woo evangelicals.
The people who have real money riding on Mr. Romney's choice have mostly lined up behind Rob Portman, a first-term Ohio senator who appears as colourless as he is said to be competent. According to the online market Intrade, which allows investors to bet on political outcomes, Mr. Portman has a 33-per-cent chance of becoming the VP candidate.
Personal qualities aside, it is easy to see why Mr. Portman is the statisticians' current favourite: No Republican has ever won the presidency without winning Ohio.
A Romney-Portman ticket might amount, as comedian Stephen Colbert recently quipped, to “the bland leading the bland.” But it would be in keeping with Mr. Romney's button-down style. Mr. Portman has a solid résumé and is unlikely to ever go rogue.
The vice-president is first in the line of succession to the Oval Office and its nuclear codes. Mr. Romney's aides have made it known he does not take that fact lightly.
Neither, as Mr. McCain found out, do voters.
Pundits have long debated whether any running mate can actually help a presidential candidate win the White House. But most agree that the wrong pick can be a drag on the ticket. Mr. McCain's campaign imploded after his outspoken but poorly briefed partner unravelled en route to election day.
In picking Ms. Palin, who had been governor for less than two years, Mr. McCain raised questions about his judgment. As she stumbled through interview after interview, voters wondered if Mr. McCain had made a rash choice just to get a bump in the polls.
Worse still, they began to ask whether he might do the same as president.
Mr. Romney will not make that mistake. He assigned Beth Myers, the long-time aide who knows him best, to lead the vetting process. Despite rampant rumours, Mr. Romney insisted last month that only he and Ms. Myers know who is on the short list.
Ann Romney, Mr. Romney's wife, recently suggested she also was playing a role in the selection process, adding she would “love [the] option” of picking a woman. But the odds makers are so far betting on an all-testosterone ticket.
Mr. Romney took the unusual step last month of revealing that Mr. Rubio was being “thoroughly vetted” amid media reports that the 41-year-old senator was off the list.
Mr. Rubio's fans insist he would improve the Republican image among Hispanic voters, an increasingly critical block of the electorate. But his short experience in Congress and questions about his past – for starters, he is accused of fudging the details of his family's flight from Cuba – could make him too risky for Mr. Romney's taste.
As for the other possibilities, indications might be gleaned by watching Mr. Romney on the campaign trail, where Mr. Portman, former Minnesota governor Tim Pawlenty and New Hampshire Senator Kelly Ayotte have been most often at his side.
In other words, not a Palin in sight.