Replacement Theory is the anti-Semitic Catholic belief, which has suddenly resurfaced, that Jews are no longer God's chosen people, but rather Christians, a belief expressed by anti-Semites like Tucker Carlson. 

The Jews are the chosen people, as are God's promises to the chosen people. "The last I checked, Jesus was a Jew. I am proud to be a Christian Zionist."

He then added that the Republican Party is organizing against the anti-Semitic rats that have infiltrated it.