Washington (CNN) -- Vice presidential candidates may be chosen for different reasons, but they all have one main job: show up where the main guy can't.
By that count alone, two potential running mates for Mitt Romney will get some real world experience this week in two key states.
While his home state of Wisconsin is the center of the political world Tuesday, Rep. Paul Ryan will be a thousand miles away helping out the Romney campaign. The House Budget Committee Chairman will be at a roundtable put on by Team Romney in Raleigh, North Carolina at Big Ed's City Market.
Meanwhile, Romney will head to Texas, where he has a small business event and a fundraiser Tuesday.
Sen. Rob Portman of Ohio stays closer to home for his turn helping out the campaign this weekend. He will be the star attraction at the Columbus opening of a Romney for President campaign office Saturday.
Ryan and Portman's events are part of the Romney campaign, but other possible vice presidential contenders will have a high profile stage of their own this week.
New Jersey Gov. Chris Christie, Louisiana Gov. Bobby Jindal, Sen. Rand Paul of Kentucky, and former Romney presidential opponents Rick Santorum and Michele Bachmann all speak Friday at the Conservative Political Action Conference in Chicago.
What about the guy who has that #2 job already? Well, Vice President Joe Biden attends a Democratic Senate Campaign Committee fundraiser in suburban Washington Tuesday. On Wednesday, he makes an "official" White House trip to North Carolina, selling the president's jobs and middle class economic plan in Winston-Salem.
It may be an official trip, but it's no coincidence that it will mark his second trip in two weeks to the state that hosts the Democratic National Convention, as Republicans try to recapture the presidential vote there.
Biden speaks on the administration's behalf while the president heads to California fundraisers.
Different roles, same job description.