The question that needs to be asked is how do people who are NOT wealthy, take a job paying a modest salary and then suddenly become wealthy during their time in office?
I think the better question is what are the mechanics of the wealth gain?
Like if you're in the house for eight years, I expect you to become considerably more wealthy. But I also assume everyone I know with a stable job is going to become considerably more wealthy. I assume any couple where one member makes $174,000 per year should build wealth.
Then we have questions of expenses. I assume when you're in congress, your job pays for a lot. Food, transit, some other daily nonsense. So likewise, I think a person who lacks those expenses has an edge in building wealth.
There's also assets. If you move to DC, you might buy a home. After 8 years, a home in DC has likely appreciated a good bit. Same for if you go to congress at 45 and own a few properties already. They'll gain value because that's what happens.
Then there's the matter of a spouse. If you spouse has a job, that's also kicking in. At that salary, you could max out a 401k, so you're up $160k right there, plus growth. If you have a spouse with a high-powered job, even more so.
Plus you have books, speaking fees, the general set of opportunities that come with being famous and important (thankfully, no sponsorships yet).
That's not to say some, maybe many, congresspeople are not lining their pockets illicitly. But it's also hard to parse these things. If the spouse has a high-powered job, that builds wealth. But that's not something that's all that complex.
So to circle this around, there is some form of getting wealthy that all these people should be doing with sound financial sense. The question is, what is the baseline and what are signs someone is grossly exceeding it.