Republican Congress used to be an Oxymoron

The US Senate is a conservative institution, by design. It empowers land over population, giving equal representation to Wyoming (600 thousand) and California (38 million)

The Senate was designed as a check against the excesses of democracy.

The House of Representatives is designed to represent what "the people" really think. California has 53 Representatives to Wyoming's one. There are a few counter examples, like Rhode Island versus Texas, but in general the party that represents rural interests must have relatively more representation in the Senate than it has in the House.

This has always been the case... until the 1990s. For the last 20 years the House has generally been Republican while the Senate has generally been Democratic.

One word. Redistricting.

The House can be gamed. The Senate cannot. The Senate is pre-gamed by the long-standing unequal divisions of state borders but it can not be manipulated further. The House, however, can be twisted into whatever form State legislatures wish, including promoting the interests of a national Party over the interests of the State itself.

And State legislatures are themselves unequal. Being typically based on the federal model they promote rural interests disproportionately to urban interests.

By concerted national Party effort the natural conservatism of state legislatures can be bootstrapped into an almost permanent congressional majority to the point where the most representative part of the US government, by design, becomes the least representative.

I grew up in a world where the House of Representatives was guaranteed to be liberal, by wide margins, while the Senate and the Presidency were conservative-leaning. (The electoral college is designed to be unrepresentative by incorporating the inequality of the Senate. Wyoming 3EV. California only 55EV.)

The only possible way for the House to be more conservative than the Senate and the Presidency is through manipulation of the fact that the House, alone in the federal government, can be manipulated through creative, biased districting.