The Survivors (1983 film)

It stars Walter Matthau and Robin Williams, with supporting roles by Jerry Reed, Kristen Vigard and James Wainwright.

That night, the robber (named Jack Locke) visits Sonny's house to kill him and his teenage daughter, Candice, but Donald saves them.

He buys several guns, leaves his girlfriend, and goes to a Vermont "survival camp" led by a man named Wes.

Donald, however, is so confident of his ability to face danger that he taunts Jack into coming up to the camp for a final showdown.

[1] Pauline Kael's review in The New Yorker: The banner line on the ad says 'Once they declare war on each other, watch out.

The Survivors isn't about two men declaring war on each other; it's about two New Yorkers without anything in common who become friends.