WASHINGTON -- Will he go safe or go sexy?

Republican presidential candidate Mitt Romney is poised to pick a running mate, the most important decision of his campaign to date.

Will the cautious Romney try to shake things up by tapping someone such as Sen. Marco Rubio, R-Fla., or former Secretary of State Condoleezza Rice, among a group of minorities and women who could add sizzle to a ticket some Republicans fear will be bland?

Or will he stay in his comfort zone and select a steady, but buzz-challenged, running mate such as former Minnesota Gov. Tim Pawlenty or Sen. Rob Portman of Ohio?

Romney’s search has been a cloak-and-dagger operation. He lifted the veil only a tiny a bit this week, telling the National Review that he might consider, “in some cases, people who provide perspectives and skills that I may not share.”

In a signal he’s getting close, he’s put a staff in place this week to help the new candidate. Randy Bumps, former political director for the National Republican Senatorial Committee, will be the vice presidential candidate’s operations director, and former party spokesman Kevin Sheridan will be his communications director.

Romney, aides say, knows well the first maxim of picking a running mate: Do no harm.

"If there is a game changer, it would be rather remarkable," said Andrew Kohut, president of the Pew Research Center.

What the ticket mate can do is make a difference at the margins

Lyndon Johnson is widely credited for delivering Texas to John F. Kennedy in the close 1960 election. Pawlenty, Portman, Rubio and Sen. Kelly Ayotte of New Hampshire all have that swing state potential in 2012.

"If Rob Portman can add two points in Ohio, for instance, that would be substantial,” said John Pitney, a professor of government at Claremont McKenna College in California

That doesn’t happen often, though.

Several recent picks stirred strong opinions and produced mixed results: Richard Nixon’s choice of Spiro Agnew in 1968, Gerald Ford’s pick of Bob Dole in 1976, Walter Mondale’s 1984 selection of Geraldine Ferraro, George H.W. Bush’s 1988 choice of Dan Quayle, and John McCain’s pick of Sarah Palin in 2008.

Nixon and Bush won. The others lost, but few historians blame their running mates for their defeats – and note that often the excitement or controversy they generated had little to do with the result. Ferraro, for instance, was a hero to millions of women, the first woman on a major party ticket. But women that fall went 58-42 for rival Ronald Reagan, who won in a landslide.

Palin is regarded as the poster child of recent poor picks. Election Day exit polls showed 60 percent of voters thought she was not qualified to be president; that group voted 82 percent to 16 percent for President Barack Obama.

Yet no poll suggests she was the key reason for McCain’s loss, and some McCain campaign officials insist that the former Alaska governor succeeded in exciting a conservative base leery of McCain.

“What he (Romney) shouldn’t repeat with his pick is the way she was handled,” said Steve Duprey, a New Hampshire Republican Party official who accompanied McCain throughout the campaign. “She didn’t have a great initial interview and we didn’t roll her out enough initially to the press.”

Here’s a look at the potential VP candidates: