In a sign that appointed Sen. Michael Bennet (D) may have put any talk of a serious 2010 primary challenge behind him, fellow Colorado Sen. Mark Udall (D) endorsed Bennet on Saturday.

“In only a matter of months, he’s making his mark,— Udall said in a statement “He has impressed colleagues from both parties for the depth of his intellect, his capacity for hard work and a reputation for effective leadership.—

Bennet is coming off a solid first quarter of fundraising — he raised $1.3 million by the end of March — and he benefits from the fact that Republicans have yet to find a candidate.

Aurora City Councilman Ryan Frazier (R) has gotten into the race, as has Weld County District Attorney Ken Buck (R) and businessman Cleve Tidwell. Former Rep. Bob Beauprez and radio host Dan Caplis are other GOP possibilities.