Did Trump say “America First” at St. Clair County, Michigan?

Yes. Said at 5:13:49 PM ET, flagged live 0.33 seconds after the word.

“And a Republican Senate on November third we will continue to put America first every single day always”

From Saidwire’s live log of Trump rally · St. Clair County, Michigan. All 13 words said at this event.