Take a look at the electoral map for 2012 at 270towin.com. If Romney wins FL, NC, VA, OH, and IN, he still loses unless he wins an additional state. Go to Wikipedia and sort the results by state for 2008 in order of increasing Obama vote percentage. After these five states, the state that Obama won by the least was Colorado. Unfortunately, Colorado does not have a sitting GOP senator or governor, and the odds are really long that Wayne Allard, the former senator who did not seek re-election in 2008, could tilt the state to Romney given that Colorado elected Michael Bennet to the Senate in 2010.
The great state of Iowa is the next state on the list. Terry Branstad is a Republican and he is the governor of Iowa. He has won FIVE elections for governor, starting under Ronald Reagan in 1982. He took a break from being governor and got elected for the fifth time in 2010 after having been out of office for more than a decade. He served in the Army in Vietnam. He's got a lot of experience and if voters in Iowa didn't like the results, they wouldn't keep voting for him. As a corollary, he's been thoroughly vetted already.
I don't know how conservative he is and I'm well aware that he doesn't energize a room like 'The Won' did in 2008, but after having experienced life under a flashy leader with no substance, I think that voters could really go for a moderate, mild-mannered guy from the Midwest they trust in 2012. Iowa likes to vote for him and his presence on the ticket probably wouldn't hurt in Missouri or Ohio. Play with the electoral map. It is pretty hard to see a scenario in which Romney wins Iowa but loses the election. I also like the contrast of sending two governors up against two senators in the general election.
The next states in ascending order of the extent of Obama's margin of victory in 2008 are Minnesota, New Hampshire, Pennsylvania, and Nevada. Mark Dayton narrowly won election as the DFL governor of Minnesota in 2010 with the sideshow of an Independence Party taking 11.94% of the vote. Additionally, Al Franken, a man who wrote a book about how he won the presidency by running a campaign entirely against ATM fees, is representing the state in the Senate. I wouldn't hold my breath on the ability of Tim Pawlenty to flip this state for Romney.
New Hampshire holds slightly more hope with its 2010 split decision election of Kelly Ayotte to the Senate and the Democract John Lynch as Governor. I think that Kelly Ayotte is too new to high office for consideration and that both the younger John Sununu, despite not having being re-elected in 2008, and Judd Gregg, despite flirting with joining Obama's cabinet, would be considered better qualified than her at this juncture. There is something to be said for attempting to win via a New England strategy given New Hampshire's status as the regional tax haven and the fact that it worked for GWB in 2000, but it seems exceedingly risky.
I'm not sure what to make of the election in of Pat Toomey and Tom Corbett since the state hasn't gone for a Republican nominee since 1988, in contrast to Iowa, which went for GWB in 2004. An election year in which Pat Toomey could swing Pennsylvania to Romney is most definitely an election year in which Romney does not need to win Pennsylvania in order to win the presidency.
Turning next to Nevada, we see a state that Obama kicked in the teeth with his bashing of corporate conferences there. Brian Sandoval is the freshly elected GOP governor there, and prior to this he was a federal judge. Picking him as a running mate would be a be an interesting proposition. He is new to his current office, but I tend to think that his four years on the federal bench would bring something both serious and novel to the executive branch. I also expect that a federal judge would mop the floor with Joe Biden in a debate. He's also of Hispanic ancestry. He could be a game changing pick, but he is new to the governor's office, so it would be a bit risky.
If you look at Mitt Romney, he appears quite vital. A lifetime of clean living has kept him youthful. This doesn't change the fact that he's 65. We need an experienced VP who can be trusted to take charge if nature should take its course too early. There are a lot of exciting new officeholders such as Ron Johnson, Marco Rubio, Rick Snyder, Susana Martinez, Bob McDonnell, Kelly Ayotte, and Nikki Haley who show great promise for the future but two years of experience in high office leaves something to be desired. If elected to the Senate this year, Ted Cruz might even be formidable in 2016. Rob Portman previously served in Congress and the cabinet, so being new to the Senate isn't a handicap for him. Pat Toomey's prior service also mitigates his short tenure in the Senate.
In summary, Romney needs to win a state that Obama won in addition to FL, OH, VA, NC, and IN. I think that Iowa, Nevada, and New Hampshire are the best targets. We cannot allow Obama to be re-elected, but I expect it to be a very close race. There are quite a few people in this country who could competently serve as commander in chief, but there are not many who could help thread the needle to win an additional state in 2012. I view winning Iowa as the most achievable scenario and the selection of Governor Branstad as Romney's running mate as the most direct route to effect that outcome.