Scarborough said he doesn't want to return to politics right now and instead will renew his contract with NBC to host "Scarborough Country" on MSNBC.
"When party leaders approached me three weeks ago, I told them how difficult a campaign would be this year considering my personal and professional commitments," Scarborough said. "Besides, I never cared for candidates who had to be coaxed into a political battle. Either you feel it in your gut or you don't."
Scarborough cited his show, which is taped in his hometown Pensacola, and his desire to be at home while his youngest son finishes high school.
The National Republican Senatorial Committee, led by Sen. Elizabeth Dole (search) of North Carolina, had tried to talk Scarborough into challenging Harris. He had planned to talk with White House and Republican National Committee officials this week about the race.
Republicans fear that Harris won't be able to attract enough Democrats and independents as she challenges Democratic incumbent Sen. Bill Nelson (search). She drew national attention during the 2000 presidential election recount when she was Florida's secretary of state.