Sen. Michael Bennet (left), Colorado Democrat, listens to his Republican challenger, Ken Buck, during a debate on "Meet the Press." Mr. Buck insisted that he hasn't abandoned conservatives in favor of appealing to moderate voters. (NBC via Associated Press)

Photo by: William B. Plowman

Sen. Michael Bennet (left), Colorado Democrat, listens to his Republican challenger, Ken Buck, during a debate on "Meet the Press." Mr. Buck insisted that he hasn't abandoned conservatives in favor of appealing to moderate voters. (NBC via Associated Press)