The republicans were able to gain control of both houses of congress in 1946 because of

The Republicans snatched back the house of the senatorial for the initial 6 years during Reagan leadership, while the Democrats held the House. Since 1988, in 15 Congressional races, the Republicans have held the lion's share in the whole Congress multiple times on Election Day and the Democrats numerous times.

After the 2000 political decision, the Democrats increased a choosing vote in the Senate after a Republican turned into an Independent in May 2001.

that is probably something for you to answer