Via BuzzFeed:

Arizona Senator John McCain, his party’s 2008 nominee, will endorse Mitt Romney in New Hampshire tomorrow, a well-placed former McCain aide told BuzzFeed Tuesday.

McCain and Romney were bitter foes in 2008, but Romney repaired the relationship after his defeat with a season of determined campaigning for his former rival.

The endorsement will offer the Romney campaign a huge story after a tight and ambiguous finish in Iowa.