Brown's campaign proposed canceling the Tuesday night debate on Monday afternoon, as it became clear that the damage from Hurricane Sandy would take much of the day and evening Tuesday to manage. Warren's campaign followed shortly after in agreement.

As of early Tuesday morning, WGBH, the station hosting the debate, was still trying to reschedule, and on Tuesday afternoon Warren's campaign proposed the final debate be held on Thursday night.

But Brown's campaign issued a release late Tuesday night explaining that the senator wouldn't have time during the final week for a debate, citing a bus tour he plans to launch on Thursday.

"With only days remaining in the campaign, and with a long-planned bus tour kicking off Thursday through Election Day that will take Scott Brown to every corner of the Commonwealth, our calendar simply cannot accommodate a rescheduling of this fourth debate and the planning and preparation that would go into it. Senator Brown is pleased to have participated in three major televised debates, and regrets that Professor Warren refused two additional earlier debate opportunities that he accepted," said Brown communications director Colin Reed.

Warren's campaign shortly after released a statement from campaign manager Mindy Meyers slamming Brown for declining to debate.

"Unfortunately but not surprisingly, Scott Brown is again ducking questions about his record voting on the side of big oil and billionaires and against equal pay for equal work, against a pro-choice Supreme Court Justice and against insurance coverage for birth control.  Elizabeth agreed to additional debates that Brown refused in Worcester and the South Coast as well as a forum hosted by the NAACP.  Scott Brown doesn't want to have to talk about his record — plain and simple," the statement read.