Trump’s debate performance gives Democrats reason to worry

...Democrats have enjoyed the summer of Trump and hope it lasts long enough to inflict serious damage on the Republican brand. But they no doubt saw enough Thursday night to begin to worry about what a general election pitting a vulnerable Clinton against one of the non-Trumps could portend.

On Thursday, a national television audience — likely a record primary-debate audience — got its first real look at candidates such as Sen. Marco Rubio of Florida, Ohio Gov. John Kasich, Wisconsin Gov. Scott Walker, Sen. Ted Cruz of Texas, New Jersey Gov. Chris Christie and Sen. Rand Paul of Kentucky. Even former Florida governor Jeb Bush probably isn’t that well known, despite his familiar name.

In a field of 17 candidates, Trump’s poll numbers are impressive. He’s getting a fifth to a quarter of the GOP vote in national polls and has strong numbers in both Iowa and New Hampshire. In the national polls, his nearest rivals are drawing half or less of his support.

To Trump, that already makes him a winner. But the Republican race will not remain a 17-candidate scrum indefinitely. When it opens up, Trump will find himself in a different battle, and it will probably not be as favorable to him as this summer’s contest has been...