The candidates talked about the people they met on the 'campaign trail'. [=the people they met while going to different places during the campaign]
As he gained more political power, he left a 'trail' of bitterness behind him. [=he treated people badly and made them feel bitter]
The police are 'hot on the trail of' the escaped convicts. [=are chasing the escaped convicts and are close to catching them]
(..) - Took 'em out with a heat seeker. - There's something else, Major. This is no ordinary army taxi. It looks more like a surveillance bird to me. - Pick up the trail yet? - Billy's on it. Heat seeker, Dillon. Pretty sophisticated for a bunch of half-assed mountain boys. I guess they're getting (..)1987 Predator
(..) get squeezed and we can't let that happen. We need the best. That's why you're here. - Go on. - Simple setup. One-day operation. We pick up their trail at the chopper, grab those hostages, and bounce back. - What do you mean, "we"? - I'm goin' in with you, Dutch. You know that. (..)1987 Predator