MIAMI (AP) — On the spur of the moment, a singer in a Cuban salsa band had an idea for a lyric to please fellow Trump supporters at a Miami birthday party.

Tirso Luis Paez flicked his hand so his band mates would let him take over during a crowd favorite, "Cuba is Me," and instead of singing the usual chorus, he belted out: "Yo voy a votar, por Donald Trump!"

The seemingly spontaneous moment with Los 3 de la Habana was live-streamed and soon viewed by tens of thousands. The Trump campaign quickly featured it in a national ad projecting Miami Cuban enthusiasm for the Republican leader to Latino...