Trump assumes that the Republican electorate is representative of the national electorate. It’s not. Take the Muslim ban. Sixty-eight percent of GOP voters support it. Only 38 percent of Democrats do. And there are approximately 7 million more Democrats in the country. (Independents are split 51-40 in favor.)

The other major example of doing what’s always worked is the ad hominem attack on big-dog opponents. It worked in the primaries. Trump went after one leading challenger after another, knocking them out sequentially.

Hillary Clinton is a lousy campaigner but her machine is infinitely larger and more skilled than any of Trump’s 16 GOP competitors. More riskily, Trump is now going toe-to-toe with a sitting president.

Barack Obama is no Jeb Bush. He’s not low energy. He’s a skilled campaigner who clearly despises Trump and relishes the fight. And he carries the inestimable advantage of the gravitas automatically conferred by seven and a half years of incumbency. Moreover, he now enjoys an unusually high approval rating of around 53 percent. Trump’s latest favorability is 29 percent (Post-ABC News).