Practically speaking, turnover in the US Senate is pretty low. Thomas Benton wrote a memoir called Thirty Years in the Senate of the United States, when that was a very long tenure. Chuck Grassley is in his 41st year, and has talked of running again. Mitch McConnell is in his seventh term.
"We previously listed some of the most admired leaders of both the left and the right and we noted that all of them came from safe seats. In the case of someone like Margaret Thatcher, it was a deliberate choice to give her a Tory safe seat. And safe seats help create great leaders, since it allows those leaders to focus on leadership, rather than having to think about elections. In other words, over the last 300 years, to the extent that the democracies have had good leadership, this has been achieved through a bit of engineering, where the system grants certain leaders lifetime posts, while pretending to do something different."
OK, but how's that working out in the US Senate, or even in the House? It has worked out, at times in the past - there was decent leadership there on occasion. But at the moment, we still have people who pretty much have safe seats, but the leadership is... rather lacking.
Exactly the same as Margaret Thatcher and Winston Churchill, everyone eventually faces some defeat and decides they are old enough that it is time to resign.
That's the thing that is missed about the US's governmental system. The House of Representatives has quick turnover, the Senate slower, and the Supreme Court, slowest. And their terms are staggered. It's all by design. It's tragic that the US and the UK are trying to turn the Senate and House of Lords into the same body as the House of Representatives and House Commons, respectively. It breaks a check on power and a pillar of stability.
I don't think that design ever expected a class of professional politicians who spend their lives in office. I think the expectation was that people would serve a few terms as a service to the Country then return to their private lives, not dictate policy for entire generations.
For that to work, it would need the House to encourage frequent turnover every two years. This could be done by having more Reps with each having fewer constituents, so each Rep has less influence and power. It was like this, until the lobbyists realized that too many Reps would be difficult to control and influence so the size of House was capped in 1929.
https://www.pewresearch.org/fact-tank/2018/05/31/u-s-populat...
