Donald Trump argued that radio host Glenn Beck -- who has endorsed Ted Cruz -- can't vote for Cruz in his state's primary Saturday because he is no longer a registered Republican. For Trump, this provides proof that Beck is "dumb as rock." "Word is that crying @GlennBeck left the GOP and doesn't have the right to vote in the Republican primary. Dumb as a rock," Trump tweeted Saturday. If true, this would serve as rich irony for many observers. Trump has been hit for his fleeting party affiliation history, but is, by all accounts, currently a registered Republican in...