Per this, Mitt Romney has endorsed John McCain:

Romney, a 2012 presidential aspirant, famously tangled with McCain on the campaign trail in 2008, and has some indirect ties to Hayworth -- Maricopa County Sheriff Joe Arpaio, one of Hayworth's biggest boosters, served as honorary chair of Romney's Arizona campaign team in 2008, while Jason Rose, an advisor to Hayworth's Senate run, was Romney's state director.

On Tuesday, however, Romney had nothing but effusive praise for McCain, saying "I'm proud to call him my friend."