Meanwhile, McCain adopted a tough tone on illegal immigration in a radio ad airing in Southern California. The ad appeared to be aimed at countering Romney's criticism of his conservative credentials and his stance backing a path to citizenship for illegal immigrants, an issue that has strong resonance with Republican voters in the state. "I've listened and learned," McCain said in the ad. "As president, I'll hire new border guards, build a fence, ask governors to certify that their borders are secure. The two million people who have committed crimes will be deported immediately. "No one will be rewarded for...