Embattled Democratic candidates in Wisconsin joined President Barack Obama at a rally Tuesday, urging the 17,000 college students in attendance to get energized to ensure Republicans don?t have an enthusiasm gap in the midterm election. “We can?t sit this one out,” Obama told the crowd packed onto an outdoor mall in the middle of the University of Wisconsin?s campus. Another 9,000 people showed up but couldn?t fit into the mall, according to university police.