Posted Jan 4, 2012 12:00am EST

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 pivot point after the virtual tie with Senator Rick Santorum in Iowa, and a growing impression that the former governor is uniting the party behind him.

McCain is unlikely, however, to appeal to the conservative Republicans who are skeptical of both men, and may even intensify the alienation of a vocal group of grassroots conservatives.

Two Romney aides and McCain's spokesman did not respond to inquiries about the planned endorsement.

A source said a key intermediary was Ambassador Rich Williamson, a former senior Bush Administration foreign policy official who was a top advisor to McCain and now holds a senior position in Romney's foreign policy team.

Romney heads to New Hampshire tomorrow for two town hall-style meetings, a format that was McCain's signature in a state that nearly boosted McCain to the nomination in 2000.