Liberal pundits are already fanning out in force to attack and discredit Paul Ryan. Michael Tomasky, who recently wrote a Newsweek cover story calling Mitt Romney a “wimp,” has now decided that Romney’s bold move is “a terrible choice” because Ryan has proven himself to be an extremist on budget issues. No doubt there are many Democrats rubbing their hands in glee in contemplation of reviving some version of the ad that featured an actor playing Paul Ryan pushing a grandmother in a wheelchair off a cliff. But the smarter ones are worried. First, if Ryan is an extremist and...