A Republican-leaning outside group is investing in Nebraska's suddenly tighter Senate race.

American Crossroads, the group organized by Republican operative Karl Rove, is spending $420,000 on the race between Republican Deb Fischer and former Democratic Sen. Bob Kerrey.

The race has been considered a clear Republican pickup after Sen. Ben Nelson announced that he would not seek another term, but recent polls have showed a closer contest.

Nate Hodson, a spokesman for American Crossroads and Crossroads GPS, said they will unveil the ad on Wednesday.

Crossroads GPS also is investing $512,000 in New Mexico, where Democrat Martin Heinrich has held a lead in polls over former Rep. Heather Wilson.