Republican presidential candidate Donald Trump may be the rare breed of political prizefighter who warns his opponent exactly where he's going to throw a punch - and yet still manages to land the blow, more often than not.Take, for example, Trump's recent decision to raise questions about whether Texas Sen. Ted Cruz's Canadian birthplace could endanger his presidential candidacy. Cruz has laughed off Trump's suggestion - but he can't say he didn't see the attack coming. The outspoken billionaire offered fair warning that he might come after Cruz if the Texas senator began to rival him in primary polls."I noticed...