The Kennedys pushed for banning European immigration and maximizing non-European immigration in the 1960s.
The big change came with the immigration law passed in 1965, as I recall, pushed by Teddy Kennedy.
The idea was voters of European descent were rejecting the Democratic party, so they did not want to allow more anti-communist Europeans to enter the USA.
That is the theory.
The left says they just wanted to help people...
Note that the Biden administration rejected the idea of allowing white, South African farmers to get refugee status. Probably because they would reject communism too.
You don’t help people by cutting their throats & telling them it’s good for them.