Listening to 29 adults talk about Donald Trump for 2 ½ hours probably isn’t anyone’s idea of fun, especially when the talkers are Trump supporters to one degree or another. But it can be illuminating.

And a focus group of Trumpies on Monday night in Alexandria, Virginia, was just that—quite revealing. It was organized by Frank Luntz, Mr. Focus Group himself. He’s conducted more than a thousand of them. Yet he was at times surprised by how the gang of 29—17 women, 12 men—talked about Trump.