Donald Trump is taking aim at Republican presidential rival Sen. Ted Cruz, a tactical shift that could be risky on two fronts: It may have come too late, and the Texas senator might actually be benefiting from the attacks...... For Mr. Cruz, being under attack by other Republicans is a badge of honor, another backer said. "It's a quasi-endorsement of Cruz to the grass roots," said Saul Anuzis, former Michigan GOP chairman. Polls show a growing number of Trump backers see Mr. Cruz as their second choice. Cruz spokesman Rick Tyler said that when the campaign began, polls showed that...