Gingrich, Graham and Rubio would in some ways resemble the Joe Biden model of the vice presidency. Biden struggled in his 2008 campaign with voters, but he is popular with Democratic insiders, from civil rights leaders to labor union heads. And much of a vice president's job is behind-the-scenes, shoring up support for a president's initiatives with members of Congress and interest groups. Graham has served in Congress since 1995 and has deep relationships with military leaders, the press and other Republican officeholders.