Bradley told local news outlet WMUR that he's decided against a run because of family health issues.

"Family comes first," he said.

Bradley was considered a top GOP contender for either the Senate or the governor's race in 2014, and his decision not to enter the race now leaves Shaheen without a challenger. A handful of other New Hampshire Republicans are considering it, but none have the profile and fundraising base that Bradley commands.

Former gubernatorial candidate Karen Testerman, a conservative activist in the state, is exploring a bid, and former state Sen. Jim Rubens is also looking at a run.

Former Massachusetts Sen. Scott Brown (R) hasn't yet ruled out a run and has made a number of stops to the state in recent months — but local Republicans have been skeptical that he'd be competitive against Shaheen, who remains popular, according to recent polls.

Bradley did leave the door open to a congressional bid or a run for reelection to the state Senate. Republicans believe New Hampshire Democratic Reps. Ann McLane Kuster and Carol Shea-Porter could be vulnerable this cycle.