Peggy Noonan, this morning in the Wall Street Journal:
A continuing mystery of Mr. Trump is his failure to impose on himself political discipline. He has been front-runner for six months but he doesn’t act as if he has absorbed the fact that he could become the nominee. At this point he owes it to his country—he owes it to his own ambition!—to become disciplined in terms of statements and policy. It is possible for candidates to be vivid but careful, dramatic but responsible. When you’re winning you can’t just keep pulling it out of your orifices. Mr. Trump’s lack of discipline should worry his supporters. I know it doesn’t, but it should. Because indiscipline shows disrespect. And people pick up on it, they see it.
It is odd too that, as the longtime front-runner, he doesn’t attempt to reassure those who will have some impact on his future, such as state and national party leaders. In his daily actions he could continue to excite his base while subtly signaling to party elders that while he might be an unusual nominee he would, in some recognizable way, be a responsible one. Instead he ties them in knots each day and embarrasses them. That limits his popularity, lowers his ceiling of support, and reinforces the idea he’s an impetuous flake.
He tweets out taunts alerting party stalwarts to his continued popularity in the polls, and noting that while he does not intend to go third-party he certainly could. This is a form of blackmail: Nice little party you’ve got here. Shame if someone blew it up.