LAS VEGAS -- Nevada Sen. John Ensign apologized to Republican colleagues Tuesday for having an affair with a former staff member.

Senators leaving the GOP's weekly policy lunch described the senator as somber and apologetic during the closed-door session, and that most of his colleagues accepted his mea culpa.

After admitting last week that he cheated on his wife, Ensign resigned from his post as chairman of the Senate Republican Policy Committee.

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Speculation that he will run for president in 2012 immediately quelled following news of the affair, and a recent Las Vegas Review-Journal poll found his approval rating has dropped 14 points to 39 percent.

Ensign also faces the possibility of an ethics investigation after a watchdog group said it would file a complaint with the Senate Ethics Committee.

A spokesperson for the senator said last week the admission of the affair came after the husband of Ensign’s mistress, Doug Hampton, made demands for “cash and other financial benefits.” That spokesperson stopped short of using the word extortion.