Greg Sargent: Say it again, Mitt Romney: Trump is unfit to serve

It is a useful confluence of events that President Donald Trump issued a tweet about nuclear weapons that many experts regard as perhaps his most dangerous and crazy tweet yet at exactly the moment that Mitt Romney is considering a run for the U.S. Senate from Utah.It is useful because a Romney run — and victory — could set an example for other congressional Republicans to follow when it comes to acting as a check on Trump’s many excesses, from his dangerous international blust