If there was one theme on today's Morning Joe, it was Joe Scarborough's relentless, merciless mocking of the notion that Marco Rubio has an electoral "firewall" in Nevada. It began with Mika Brzezinski's citing of a National Review article from December that spoke of such a firewall. Joe, butter not melting in his mouth, turned to Mark Halperin, coyly wondering why he was laughing at the notion. Halperin opined that, in fact, Donald Trump was likely to carry Nevada with his biggest margin yet. Scarborough returned repeatedly to his routine, even working it into a Richard Haass report on the...