SCOTT HORSLEY: And I'm Scott Horsley. John McCain has had more time to think about his potential running mate, since he clinched the GOP nomination three months ago. McCain knows it's an important decision, even if he sometimes downplays it.
Senator JOHN MCCAIN (Republican, Arizona): The vice president really only has two duties. One is to cast a tie-breaking vote in the Senate, and the other is to inquire daily as to the health of the president.
HORSLEY: McCain's own health is good, but since he'll be 72 on Election Day, his choice of an understudy does carry some extra weight. Like Obama, McCain has tried to keep his selection process quiet. But that's only fueled speculation. Three weeks ago, when McCain hosted a barbecue at his country house in Arizona, political junkies scanned the guest list for possible running mates, despite McCain's protest it was a social event, not an audition.
Senator MCCAIN: It's just having a group of friends for Memorial Day weekend to visit us and enjoy one of the most beautiful places in America. It's no more, and it's no less.
HORSLEY: Three barbecue-goers drew special attention: former Massachusetts Governor Mitt Romney, Florida Governor Charlie Crist, and Louisiana Governor Bobby Jindal. All three have pluses and minuses. Romney would bring business savvy and roots in Michigan. But no Republican is going to win Massachusetts, where he was governor. Crist helped McCain win the Florida primary with his timely, last-minute endorsement. But McCain might be able to carry the Sunshine State even without Crist on the ticket. And Jindal, who's Indian American, would bring ethnic diversity and youth to the ticket - maybe a little too much youth. Jindal turned 37 on Tuesday. And political analyst Larry Sabato of the University of Virginia notes he's only been governor for six months.
Dr. LARRY SABATO (University of Virginia): The problem with picking someone so young and inexperienced is that it eliminates the experience argument against Obama.
HORSLEY: Minnesota Governor Tim Pawlenty is a decade older. He missed McCain's Memorial Day barbecue. He had a wedding that weekend. But Pawlenty does show up on a lot of short lists, including Sabato's.
Dr. SABATO: The attraction of Pawlenty is that he is a young, vigorous guy but has already served six years as governor. It's a swing state. The Republicans believe they have a shot at it, though it's going to be tough, even with Pawlenty on the ticket. He squeaked to a second term in 2006.
HORSLEY: Helping to carry a swing state is only one consideration, though. Personal chemistry and experience are also important. Former Congressman Rob Portman is considered a candidate, not only because he's from the battleground of Ohio but also because of his background as trade representative and with the Office of Management and Budget.
McCain could also tap someone from outside government altogether, like former Hewlett Packard chief executive Carly Fiorina.
Besides worrying about whom to pick, McCain also has to think about when to make the announcement.
Senator MCCAIN: Do you do as Bush 1 did and wait until the convention is going on and make that decision or you do it at a much earlier time?
HORSLEY: The senior Bush was just following standard practice when he named Dan Quayle on the second day of the GOP convention in 1988. Since then, Republicans have announced their picks at least a few days earlier. This year's GOP convention is not until September. There could be an advantage for McCain in waiting to see what Obama does.
McCain gets questions and advice about his choice of running mate everywhere he goes, even the White House Rose Garden.
Unidentified Woman: Sir, how would you counsel Senator McCain to choose a running mate?
President GEORGE W. BUSH: I'd tell him be careful about who he names to be the head of the selection committee.
HORSLEY: Dick Cheney ran President Bush's selection committee and ended up selecting himself. Kidding aside, Mr. Bush recommends that McCain choose someone he trusts and is comfortable with, and not worry too much about the politics.
Mr. BUSH: People don't vote vice presidents, as much as I hate to say that - for those who've been candidates for vice president. They're going to vote for who gets to sit inside that Oval Office and make decisions.
HORSLEY: Of course, many voters will get their first look at the decision-making skills of both McCain and Obama when they decide whom to put on their ticket.
Scott Horsley, NPR News.
INSKEEP: If you decide to read a who's who of potential running mates, just go to npr.org/elections. It's MORNING EDITION from NPR News.
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