For the halibut, I applied the same sort of logic the analyst applied to the Arab parties, to USian Congresspeople.

I'm not sure that really works. The politics of parliamentary systems are just different from the two-party system that results from our first-past-the-post Presidential elections. We don't have multiple parties that have to decide who they're willing to form coalitions with. (I mean, we do, but not any of material size).

That said, I think what you're describing is something that largely already happened in the United States. The great southern realignment after the Civil Rights Act. You had a ton of conservative Democrats - who had been Democrats for a very long time - who were no longer willing to be "in coalition" with the national party. And whom the national party was no longer willing to make concessions on policy issues to keep them in coalition. They moved over to the GOP.