I'm sure there are more than a few dead South Vietnamese waiting in line to have a word with Ford about how he handled North Vietnam after they broke our agreement about staying north of the DMZ after we left.
Ford could do nothing. Congress had specifically forbidden any use of U.S. Armed Forces in the Vietnamese conflict after the Paris Accords took effect. To act against the North would have meant impeachment, and Saigon just would have fell a little later.