> gerrymandering

> this means you can use the district-level gerrymander to control Senate-level seats. This has bought the GOP a ~+3-+8 bias in the Senate.

What?? No, you cannot gerrymander States (and therefore Senate seats). You can only gerrymander districts smaller than States. States with one House seat can't gerrymander that House seat either. State legislature seats can be gerrymandered. U.S. House seats in States with more than one House seat can also be gerrymandered. (EDIT: Well, I suppose if Oregon counties are allowed to move into Idaho then that would be a gerrymandering of States, but this is a very very rare event.)

The GOP might have a bias in the Senate, but that would be due to small-population States having more oomph in the Senate than large-population States. Though in 2024 the Electoral College was neutral in terms of partisan bias, which implies at most a small bias in the Senate for one or the other party.

As for gerrymandering of U.S. House districts, that has been going on since the very beginning, and even since before, since Colonial legislatures did it, and the English parliament did it before that. In fact, part of the reason for the Democrats' 62 year dominance of the U.S. House from 1933 to 1995 was gerrymandering.

But as Justice Sandra Day O'Connor explained in one of her decisions, gerrymandering is self-limiting because the party in power (in the legislature) can only optimize for seat safety (thus reducing their majority in their House delegation) or for number of seats (thus rendering some if not many of those seats not-very-safe). Since that decision we've had numerous wave elections in the House, including numerous changes in party in control of the House: 1994, 2006, 2008, 2010, 2018. Arguably in today's day and age gerrymandering doesn't count for all that much compared to the heyday of the Democratic party between 1933 and 1995.