Millions pouring into tight Senate races Nowhere is that more emblematic than Nebraska, the deep-red state where state Sen. Deb Fischer (R) had been holding a very large lead over former senator Bob Kerrey (D) in the race to succeed retiring Sen. Ben Nelson (D). Kerrey, however, has closed that gap somewhat by sharply criticizing Fischer's lawsuit against her neighbors over a ranching dispute. While Fischer is still favored, Crossroads GPS, a conservative group run by allies of Senate Minority Leader Mitch McConnell (R-Ky.), bought ad time in Nebraska to go after Kerrey to try to shore up what was once considered a sure thing for Republicans. The Nebraska ads came as part of a massive 10-state, $10.5 million campaign for the final week by Crossroads GPS, a nonprofit that does not disclose its donors. Crossroads and its affiliate, American Crossroads, had an advertising budget of roughly $100 million for 2012 to benefit Senate Republican candidates, hoping to pick up four seats to deliver a GOP majority. The U.S. Chamber of Commerce, which will be on air in four states over the last two weeks of the campaign, has a similar-sized budget for Senate races. The Majority PAC, a super PAC run by allies of Senate Majority Leader Harry M. Reid (D-Nev.), has its own final flourish of outside money. In Montana, for example, where Sen. Jon Tester (D) is locked in a neck-and-neck race with Rep. Denny Rehberg (R), Majority PAC has purchased about $900,000 worth of television ads for the final two weeks of that race, according to an advertising tracking document provided by Republicans. Across the nation, Majority PAC and its affiliate nonprofits plan to spend $7 million on Senate races in the final week, according to aides. One effect of the outside, unlimited cash has been to expand the political map at a time when, in past elections, it would now be narrowing. Crossroads and the Chamber have been advertising in three states where Senate Democrats are retiring and most experts believe the race is settled in the Democrats" favor: Maine, New Mexico and Hawaii. With such unlimited cash, the outside groups can also provide defense when a candidate goes wobbly, helping the candidate regain his or her standing and allowing the party committee to reserve its cash for the most competitive races. Just as Crossroads has poured money into Nebraska to defend Fischer, Majority PAC purchased more than $500,000 worth of ads attacking the GOP Senate candidate in Pennsylvania, Tom Smith, after Democratic Sen. Bob Casey's campaign got caught off guard by the wealthy coal executive's self-financed $17 million war chest.