S⁠⁠eth Masket⁠⁠, University of Denver Professor of Political Science is on Substack at the @smotus report. He has also written several books on political parties and factions, including
The Elephants in the Room: How Trump Voters Seized the Party from Republican Leaders,

Learning from Loss: The Democrats, 2016-2020, and

The Inevitable Party: Why Attempts to Kill the Party System Fail and How they Weaken Democracy.

Also mentioned: Furious Minds: The Making of the MAGA New Right by Laura Fields and Rachel Blum's How the Tea Party Captured the GOP: Insurgent Factions in American Politics.