What are the security concerns for Ukraine if the U.S. withdraws its support?

Ukraine's main security concern mirrors what happened with Vietnam - the fear that after U.S. support diminishes, Russia (like North Vietnam) would simply wait and then resume aggressive actions. Drawing this historical parallel, the host notes that Nixon worried about Hanoi waiting and then 'gobbling up' South Vietnam after American withdrawal. Despite different circumstances (no U.S. troops on Ukrainian ground), Ukrainians worry that any deal with Putin would be temporary. The fundamental concern is that Putin would bide his time and eventually return to aggression, much as North Vietnam did after U.S. forces left Southeast Asia. This historical lesson creates significant apprehension about any potential peace agreement's durability.