The accomplished politicians seem to struggle a bit because they have a history of being terrible. It isn't like Trump came out of nowhere - it has been most of a decade now and when he won in 2016 that was on the back of backlash that had obviously been brewing for a long time. It was notable in 2016 that he had to knock out Bushes and Clintons from the presidential race who visibly couldn't wring compelling support out of their insider status. The Bush family name was more of a serious liability because of the family history of, you know, the Bush years. Trump's most memorable line of attack on Jeb Bush was making callbacks to how bad George's tenure was (which isn't entirely fair, but it does go a long way to showcasing why being an "accomplished politician" is a handicap given how badly US policy has been playing out for the last few decades).

If the US political class had a history of success then being an accomplished politician might be a tick on the report card, but in practice it seems to mean that they have sympathies to the military-industrial complex and a number of extractive lobby groups.