The Carter administration, believing that essentially any processing of spent fuel from reactors was a proliferation threat, committed the US to an open (once-through) nuclear fuel cycle in the second half of the 1970s. Absent that decision, something like the LFTR might be much closer, as engineers sought higher burn-up rates and simpler reprocessing techniques.

I could be wrong, but I think the vote in Congress was unanimous for the ban. Carter was not the only pol at fault. The pervasive fear of nuclear annihilation made all pols accept any promise of security no matter the cost. Sort of like when almost all Congress members gathered on the steps of the Capitol after 9/11 to pray and sing God Bless America. To hell with the Constitution.