Caveat: I am a Brit so my main two parties are Conservative and Labour but the same system seems to apply. One party seems to be selected as the"main" party so for the US that I see as the Democrats. The other party is there to provide the illusion of choice.

The US and UK choose their candidates differently but the common theme seems to be that people behind closed doors choose the short list.

The main change recently is that politicians, particularly the top jobs, are specially selected for their ability to follow orders. Someone presentable but not too bright who likes money makes a good choice. Think: Johnson, Biden, Trudeau, Ardern, Sholtz, Von Der Leyen, Macron, not forgetting Zelensky, of course.