Donald Trump never laughs," Al Franken said.

This was the senator's first observation to me on a recent afternoon. It was exactly three weeks from the day the punch line became the president-elect. And Trump's mysterious absence of laughter had never occurred to me before, even though I'd spoken to him a fair amount and he has lived pretty much nonstop in our faces for 18 months, no end in sight.

Franken, the second-term Democratic senator from Minnesota and, before that, a longtime writer and performer on "Saturday Night Live," has studied this. He provided commentary for MSNBC at the Al Smith Dinner, the Catholic charity fund-raiser in October where presidential nominees engage in good-natured ribbing of themselves and each other (Trump mostly skipped the "good-natured" part and was booed). "I wanted to see if Trump laughed," Franken said. "And he didn't. He smiled, but didn't laugh. I don't know what it is."