As Ms. Cheney faces a near-certain defeat on Tuesday in her House primary, it is the likely end of the Cheneys’ two-generation dynasty as well as the passing of a less tribal and more clubby and substance-oriented brand of politics.

“We were a very powerful delegation, and we worked with the other side, that was key, because you couldn’t function if you didn’t,” recalled Mr. Simpson, now 90, fresh off being awarded the Presidential Medal of Freedom and as tart-tongued as ever about his ancestral party. “My dad was senator and a governor, and if I ran again today as a Republican I’d get my ass beat — it’s not about heritage.”…

“Everything is political in Wyoming except politics, which is personal,” Mr. Simpson likes to say. What alarms some longtime Wyoming Republicans more than campaign season tensions is what the combination of Trump fear and fidelity will ultimately mean for the strength of the delegation — and for the state’s future. Wyoming has neither a state income tax nor a corporate tax, having long relied on severance levies on oil, natural gas and coal.

With growing national support for clean energy — and a large federal bill promoting climate-friendly power soon to become law — that pillar of Wyoming’s economy could face an uncertain future.