Donald Trump has long demonstrated a knack for getting his political opponents to make fools of themselves. Sen. Marco Rubio learned this the hard way on the 2016 campaign trail when he tried to out-Trump Mr. Trump. New York Gov. Andrew Cuomo and former CIA chief John Brennan got caught in the trap last week.

Mr. Cuomo took issue with Mr. Trump’s campaign slogan, “Make America Great Again,” telling an audience full of Democrats that “we’re not going to make America great again—it was never that great.” The audience booed....