WASHINGTON -- If Haley Barbour advised Mitt Romney about whom to pick for his running mate, the former Mississippi governor might repeat something he said in a book about his home state's politics: "Never make a political decision until you have to, for things could always change."

Romney's search for a running mate will be guided by a few factors, and the individual qualities and resumes of each potential pick will play an important role. But there will be another significant element: the situational dynamics of the presidential election four months from now, when the GOP convention in Tampa begins on Aug. 27.

Will Romney be trailing President Obama in the polls so much that he needs a jolt, a game changer, a boost of energy? Or will the race be neck and neck, in a dead heat? If so, he will likely be seeking a less risky choice, someone who will not affect the race significantly in either a positive or negative way.

"How that dynamic shakes out will have a lot to do with how a vice presidential pick is made," said Taylor Griffin, a Washington-based consultant who worked in the White House for President George W. Bush and on Republican Sen. John McCain's 2008 presidential campaign.

Interviews with GOP insiders and those involved with the Romney campaign underscore the conventional wisdom: Most people expect the presidential race to remain tight, as a new New York Times/CBS News poll showed it to be on Thursday morning. If that trend continues this summer, it would increase the likelihood of a do-no-harm pick by Romney and reduce the chances that this already cautious candidate with a risk-averse campaign would go out on a limb.

"You gotta be able to win, but the second question is, how are you going to govern together?" said Henry Barbour, a Republican operative in Mississippi and nephew of the former governor. "That's why George W. Bush picked Dick Cheney because they got along; they were compatible. It certainly was not a political pick. Dick Cheney was not a guy who loved going out and campaigning, but he loved governing."

Romney, 65, is known to value loyalty and compatibility.

"Compatibility is a big factor," Barbour said. "It should be obvious ... But if you just pick somebody because you think they're going to help you win some big state or draw big crowds, I think that's a mistake."

There is certainly some skepticism at Romney's Boston headquarters about the potential impact of a vice presidential pick -- at least on the positive side. The focus, according to campaign sources and Republicans who deal with Boston, appears to be on averting the potential of pick causing Romney any damage.

The safer picks are all white men: Ohio Sen. Rob Portman, Indiana Gov. Mitch Daniels, Virginia Gov. Bob McDonnell and former Minnesota Gov. Tim Pawlenty.

The riskier picks are almost all women or minorities who are rising stars in the Republican Party but with less experience in national politics than a Portman or Daniels: This set includes Florida Sen. Marco Rubio, New Mexico Gov. Susana Martinez and South Carolina Gov. Nikki Haley.

Two white men are on the riskier list: New Jersey Gov. Chris Christie, whose weakness is that he might be so charismatic that he would outshine Romney, and Wisconsin Rep. Paul Ryan, whose budget plan is lauded by many conservatives but tough to defend in political sound-bite combat.

The one danger to Romney's taking the safe route is that the monochrome pairing of two older white men could itself pose a risk, since Romney will be trying to unseat the nation's first black president, who also happens to be, at age 50, from a younger generation.

Perhaps the only minority candidate with a substantial enough record to avoid the charge of not be prepared, should he be thrust into the Oval Office, is Louisiana Gov. Bobby Jindal.

"Daniels and Jindal would be so steady but they wouldn't overshadow him, and they wouldn't have any interest in overshadowing Romney," Barbour said. "It's not their style."

Two other outliers are former Arkansas Gov. Mike Huckabee and former Pennsylvania Sen. Rick Santorum.

Here are the pros and cons for each choice:

ROB PORTMAN

Pros: He is a 56-year-old former White House budget director (from 2006 to 2007) and successful member of Congress who remained popular with constituents during seven terms from 1993 to 2005. He also served as a U.S. trade representative to boot. Portman has a strong political network in Ohio, which again will be one of the most crucial battleground states in the election. And he is well-known for his keen mind and firm grasp of a broad range of policy issues. He served in George H.W. Bush's White House as well, so he knows how both the executive and legislative branches work.

Cons: Portman's stint as budget director under George W. Bush would open a door for Democrats to use one of their favorite attacks: Bush inherited a budget surplus from Democratic President Bill Clinton and handed a more than $400 billion budget deficit to Obama. On a more superficial level, while Portman is friendly with many in the press, he does not bring any extra charisma or excitement to the ticket. In many conservative's eyes, Portman's current position as a legislator instead of an executive (such as governor) is also a minor strike against him.

MARCO RUBIO

Pros: Rubio, 41, is a rock star. He's young, good-looking, well-spoken and a Latino. He's from the must-win state of Florida. What's not to like?

Cons: He's young and only in his second year as a senator. He would also be certain to attract a high level of scrutiny to his past, especially about whether he tweaked his family's story of leaving Cuba to make it more dramatic and if he used a credit card issued by the Republican Party to buy personal items while a state legislator. Rubio has been the most Shermanesque of all the potential VP picks in his promises to refuse any request to consider the job.

CHRIS CHRISTIE

Pros: Christie, 49, is as outsized a personality as there is in modern American politics. He loves the spotlight. He talks straighter than blunt. Some might call his a smash mouth. And voters love him. After three years as chief executive, his approval rating in New Jersey, a Democratic stronghold, is at an all-time high. He has balanced budgets in the face of huge projected deficits without raising taxes and has achieved significant reforms in the state's pension system for government workers.

Cons: He might love the spotlight a little too much for Mitt Romney's liking. He and Romney are worlds apart in terms of personal style. It would be a lot to expect him to hang back and play second fiddle. In addition, having two candidates from the Northeast limits the ticket's geographical appeal and its ability to win over rural voters. His weight is also a factor.

MITCH DANIELS

Pros: Like Portman, Daniels, 63, is also a former White House budget director. He served in that post from 2001 to 2003 and then went on to become governor, now in his second term. Like Christie, he has imposed conservative reforms as governor in budget spending, taxation and state worker salaries and benefits as well as health care. He is one of the most articulate Republicans in discussing the national debt. Also like Christie, Daniels had been wooed intensely by Republican insiders and voters to run in the primary against Romney but refused.

Cons: While Daniels served as George W. Bush's budget director, a surplus turned to a deficit under his watch, thanks in large part to a major recession caused by the September 11 attacks and major tax cuts that Bush pushed through. Daniels did not run for president because his wife and daughters (or at least some of them) didn't want him to. It's not clear whether he'll even agree to being vetted for VP by the Romney campaign for the same reasons. He also lacks the electrifying presence of a Christie or Rubio. His personality is low-key and droll. His tenure as an executive at drugmaker Eli Lilly and Co. in the 1990s would be closely examined.

BOBBY JINDAL

Pros: Jindal is another governor who has accomplished a lot that will appeal to conservatives -- cutting taxes and spending -- and taking on teachers' and state employee unions. And at 40 years old, the former Rhodes scholar is younger than other potential picks. He was re-elected in a landslide last fall and just succeeded in engineering the passage of a sweeping education reform plan by the GOP-controlled legislature. He is now taking on the challenge of trying to curb state worker pensions, though that is proving to be a tougher slog. Jindal is a former congressman (from 2005 to 2008) who in the 1990s ran Louisiana's health and hospitals system and then its university system. He is the son of immigrant parents who came to the States from Punjab, India, six months before he was born.

Cons: He is known nationally mostly for his widely panned 2009 speech giving the official Republican response to President Barack Obama's first State of the Union address. He is not seen as a particularly inspiring figure. His state, Louisiana, is already considered sure win for Romney. And there are two minor hurdles for him to surmount: First, Jindal endorsed Texas Gov. Rick Perry in the primary. After Perry dropped out, Jindal declined to endorse anyone else. And second, Jindal's Washington-based consultant, Curt Anderson, is not on the best terms with Stuart Stevens, the top strategist on Romney's campaign.

PAUL RYAN

Pros: The 42-year-old House budget chairman is a numbers-and-policy ace. He runs through the intricacies of Medicare, Social Security and budgets with the efficiency of a machine. And despite initial resistance a few years ago from many in the GOP, his detailed plan to overhaul federal spending and entitlement programs -- the biggest drivers of the nation's long-term debt –- has become essentially the party's platform. On a few occasions, he has taken on President Obama directly and more than held his own in policy debates. Being tall and good-looking doesn't hurt him. And Wisconsin is a swing state.

Cons: Ryan's "Road Map" may be accepted by the GOP as its best attempt to fix some of the nation's most vexing problems: the budget deficit and national debt. But that doesn't mean Romney and many Republicans want to make that a central issue in the race this fall. They want the economy -- and Obama's handling of it -- to be the focus. A concern is that putting Ryan on the ticket could make a plan that hasn't yet been enacted into law the central focus -- instead of what Republicans view as mistakes made by the incumbent president. This is the reason Ryan is a highly unlikely pick.

TIM PAWLENTY

Pros: Pawlenty, 51, suffered a political bruising during his time as a candidate in the primary but has emerged as a trusted adviser to Romney after he endorsed him. The personal connection between the two men should not be underestimated. Pawlenty also has an ability to connect with blue-collar voters that Romney does not. And there would be few doubts about Pawlenty's trustworthiness or loyalty.

Cons: He offers little heft to the equation in terms of geographic advantage, in that he is from Minnesota (which is not a swing state) and showed no distinct ability to excite any passion or confidence among voters during his primary run.

BOB MCDONNELL

Pros: McDonnell, 57, is governor of a key battleground state and he looks the part of vice president. He's eloquent and smart enough. He gets along with people well and seems like a natural fit for Romney. After Portman, there seems to be no other potential VP pick who is a better match for Romney when it comes to pure compatibility.

Cons: McDonnell doesn't stand out. He has not distinguished himself with any particular accomplishment or stylistic trademark. His handling of a bill requiring an ultrasound before a woman obtains an abortion was widely perceived as shaky. He first supported a transvaginal procedure before backing away from this stance and saying only an abdominal, noninvasive ultrasound should be mandated.



SUSANA MARTINEZ

Pros: The 52-year-old Texas native and granddaughter of Mexican immigrants has an inspiring, up-from-the-bootstraps personal story. The former district attorney is the first Latina to become governor in the history of the United States. She is also the head of state in a Democratic-leaning state that is nonetheless considered by some to be a swing state. Her two years in office so far have gone reasonably well.

Cons: Not much is known about Martinez. She has vowed she would turn down an offer to be considered for the vice presidential spot. And she is likely not seasoned enough to step into the vice presidential role.

RICK SANTORUM

Pros: Santorum, 53, became a hero to many conservative Republicans with his insurgent campaign for the GOP nomination, which went further than anybody ever expected. Santorum showed a talent for grassroots campaigning (that Pennsylvania campaign watchers already knew about) and a knack for articulating a conservative message that connects with voters in a way Romney never has had. He's also from a swing state, though Pennsylvania has not voted for a Republican presidential candidate since it went for George H. W. Bush in 1988.

Cons: Santorum waged a fierce and sometimes bitter battle with Romney in the primary. It's not yet clear how much the fences between the two have been mended. Santorum is holding off on endorsing Romney, waiting until he can meet with the presumptive nominee and press him to hold fast to conservative principles on key issues. How that meeting goes will likely dictate whether Santorum is even in the running for the VP spot. But Santorum's lack of message discipline and penchant for veering into social issues are likely to be turnoffs for the Romney campaign.

NIKKI HALEY

Pros: The 40-year-old governor of South Carolina is a talented, dynamic and charismatic political figure. She's the youngest governor in the country. Haley is another player among the bumper crop of young, minority stars rising in the Republican Party. She is the daughter of Sikh immigrants from India.

Cons: Haley is struggling as governor. Her approval rating is in the 30s range. Her endorsement of Romney before the Palmetto State's January primary failed to help him beat back Newt Gingrich, who won convincingly. And she is probably too inexperienced.

MIKE HUCKABEE

Pros: The former governor turned Fox News personality won Iowa during his 2008 presidential bid and attracted the same evangelical voting bloc that went for Santorum this year. The 56-year-old remains a hero to many conservatives. His name recognition is substantial, since he has been on national television regularly during prime time most weekends for the last three and a half years. He has an ability to present conservative positions in ways that are more winsome than is true for many other Republicans.

Cons: Huckabee is taken more seriously as a cultural force than as a political figure. And like Santorum, he would bring rightward drift to the ticket at a time when the Romney campaign is counting on the Republican base remaining steadfast (because of the party's intense opposition to Obama) and is focused instead on winning over independents and moderates.