"Next Tuesday, Gov. Huntsman will boycott the Nevada presidential debate, and instead hold a first-in-the-nation town hall meeting in New Hampshire, to discuss his bold plans to create jobs and reform America's foreign policy for the 21st century," said campaign manager Matt David in a statement. "While Mitt Romney's campaign has tried to game the system by encouraging Nevada to move to an earlier date, Gov. Huntsman is sticking up for the Granite State."

But Cain's departure from the primary strikes a greater blow, as the former Godfather's Pizza CEO has been tied with Romney in the most recent spate of Republican national polls. Romney was counting on momentum from Nevada and New Hampshire to carry him in the South, where his opponents have been polling higher.

Romney said earlier today that he would not join a boycott of the Nevada caucus, and is headed there Monday to open his campaign headquarters. A CNN debate is scheduled for next Tuesday in Las Vegas, although some candidates have already indicated that they are considering boycotting that as well.