Nashville (1975)

Some mysterious man is in town—very possibly Harrison Ford in a hat, although I might just be remembering American Graffiti. Somebody's staying in a motel and I think there's car racing. I was about to say Cybill Shepherd takes her top off, but that's The Last Picture Show. Is there a used-car salesman? Are there fireworks? I'm pretty sure someone tries to assassinate a senator. The part I'm most confident about is the motel and (for some reason) that the movie came out in '77.*

Looks like it was Jeff Goldbum, not Harrison Ford.
(His character's name is Tricycle Man?)

* No.