Per your second paragraph, the settings and reasons are a little more complicated for why some in Congress/Senate are a little more willing and tolerant of upending nearly 70+ years of hard-earned, difficult and cautious defensive alliances and its due to U.S. being involved in two, seemingly endless, "forever wars" in Iraq and Afghanistan for 20 years, one of which ended in complete failure and another desperate, Saigon 1975 series of moments of NGO's, Western diplomats, essential personnel, missionaries and friendly, pro-Western/American Afghans pleading at our embassy to get out. For many U.S. lawmakers and citizens, this caused a strong, neo-isolationist movement to form where we try to and remain as aloof and distant from world affairs as possible. It occured for several years after Vietnam ended under Pres. Carter which some have argued helped lead to Iranian hostage crisis and Soviet invasion of Afghanistan damaging our credibility even further.
After our experiences in Iraq and Afghanistan, this new mood or sense of neo-isolationism or non-interventionism got hijacked and exploited by bad political actors who are trying to use it for alternative purposes. I think with the current administration they believe if they can keep ignoring, deny, re-direct, or pretend these serious existential international problems don't exist, it'll eventually all just go away. I know that sounds completely and totally absurd but their ignorance, lack of awareness of the complexities behind these current issues plus its significance for Europe's and even U.S. long-term internal security tells me their that clueless or inept. They assume the world is a lot bigger and larger then it really is.