John McCain has officially inserted himself into the GOP primary race. First he publicly endorsed onetime rival Mitt Romney, and now he's weighing in on other candidates' behavior. The 2008 Republican presidential contender specifically called out Newt Gingrich for his "Romney is a big liar" comment. "You need to be careful about being too angry," McCain said on CNN. "The people of New Hampshire want to hear your views and vision for the future rather than attacks on other candidates." Perhaps Gingrich should heed McCain's advice—he is a veteran at this, after all.