Sen. Ben Nighthorse Campbell (R-Colo.) will not run for re-election in November, confirmed a GOP colleague and two well-placed Republican strategists.

Campbell was in the process of informing staff of his decision early this afternoon.

The Senator’s decision ends months of speculation about his political future that has grown to a fever pitch in recent week after the resignation of his chief of staff and his hospitalization last week for a case of severe heartburn.

Neither Campbell’s campaign office nor Senate office returned calls seeking comment.

His departure creates a wide-open race to fill the seat with a variety of possible outcomes.

Gov. Bill Owens is seen as the strongest Republican candidate. But GOP Reps. Tom Tancredo, Scott McInnis and Bob Beauprez are also mentioned as possibilities.

For Democrats, wealthy entrepreneur Rutt Birdges is in the race. But Rep. Mark Udall, who had earlier decided against challenging Campbell, is now likely to give it another look.