MESA, Ariz. (AP) —Once bitter rivals for the presidency, Mitt Romney and John McCain campaigned together as friends on Friday, one gearing up for a likely presidential bid and the other fighting to hold onto his seat in the U.S. Senate. The two Republicans fielded questions from a largely supportive audience of several hundred people, touching on issues including immigration and the environment while heaping criticism on President Barack Obama. Romney, the former Massachusetts governor, battled with McCain in 2008 for the Republican nomination for president, then aggressively campaigned for McCain in the general election. He has endorsed the Arizona...