Former U.S. President Bill Clinton (R) addresses the crowd about Kentucky's Democratic Senate candidate Alison Lundergan Grimes (L) during a campaign event at The Muhammad Ali Center in Louisville, Kentucky

Former U.S. President Bill Clinton and Kentucky's Democratic Senate candidate Alison Lundergan Grimes wave to the crowd during a campaign event at The Muhammad Ali Center in Louisville, Kentucky

Former U.S. President Bill Clinton (R) and Kentucky's Democratic Senate candidate Alison Lundergan Grimes wave to the crowd during a campaign event at The Muhammad Ali Center in Louisville, Kentucky

Kentucky's Democratic Senate candidate Alison Lundergan Grimes (R) addresses the crowd as former U.S. President Bill Clinton (L) looks on during a campaign event at The Muhammad Ali Center in Louisville, Kentucky