President Barack Obama served as the closing act Tuesday for a rock-n-roll, fire-up-the-troops extravaganza on the UW-Madison campus ? a giant rally meant to recapture the excitement of the campaign trail and bridge the so-called “enthusiasm gap” among younger, Democratic voters. Obama took the stage at Library Mall to a raucous crowd, following a performance by musician Ben Harper and a series of speeches by the state?s major Democratic candidates. From the outset, the president made it clear why he was in Madison, and on campus, at this moment.