12 years is 6 years too long. 1 term Senate, 1 term House, then get your butt back to your real job.
Elected office shouldn’t be a full time job.
The unfortunate fact is that for all too many of them, running for office is their real job.
What is detaching the people's house (US House of Reps) is not long term politicians, but the lack of representation because the number of House Seats was set in the early 19th century at 435. Exhibit 1 in my argument is California term limits has done nothing to curb the political establishment cronyism because the largest state in the Union only has 80 legislators. The money required to mount a campaign is enormous to the establishment picks the candidates and then funds them. This happens every six years.
As a comparison, my smaller state of Missouri, has 163 seats. My legislator personally knows me because he walked my neighborhood. I am on his real FACEBOOK page (not the fake political facebook) in which people post their opinion. To me, this is why my legislator represents me not because he is termed out after three years. More on this at Thirty Thousand.org
I think have great examples in our founders who intended public office to be a privilege and not a career. I think 10 years for Congress is fair, and maybe 25 years for the judiciary. The whole system is geared towards entrenched establishment politicians. The whole controversy over Trump and who he donates money to highlights this. It is a part of business for big companies and rich individuals to spread their money among two parties, which guarantees the US will always have 2 parties and the same people running them.