MSNBC confirmed Monday that has canceled conservative commentator Tucker Carlson's talk show. David Gregory, chief White House correspondent for NBC News, will host a replacement show that will air weeknights beginning at 6:00 p.m. Carlson, meanwhile, will take on the assignment of "campaign correspondent," covering the current presidential race. Carlson had come to MSNBC from CNN, where he once was the cohost of Crossfire. NBC had evidently hoped that he would attract conservative viewers who have made Fox News Channel their preferred destination. However, Carlson's program not only failed to attract those viewers, it remained MSNBC's lowest-rated evening program.