FILE - In this Dec. 6, 2011, file photo Sen. Claire McCaskill, D-Mo., speaks during a news conference about agreement over the jobs bill on Capitol Hill in Washington. Republicans? clear shot at winning control of the Senate is attracting tens of millions of dollars from GOP-allied outside groups eager to spend on a surer bet than the White House race. The U.S. Chamber of Commerce aired 10 days of ads against McCaskill and the Karl Rove-inspired American Crossroads challenged the Democratic senator as well in a concerted attempt. (AP Photo/Pablo Martinez Monsivais, File)