But it could be backtested, which I think is the point - "is the supposed insider trading actually profitable for Congress members?"

You can see the backtest performance of some of some strategies built around congressional trading data here: https://www.quiverquant.com/strategies/

The holdings and advanced metrics are behind a paywall (apologies in advance).

I think I recall someone doing that analysis and posting about it on HN, but I don't remember what the conclusion was.

There's been articles which did the math before. Several - really every few years someone takes another pass at it.

They do well. Generally, retiring their tenure wealthier than their congressional salary would allow at a 100% savings rate.

I think the question is really whether they’re trading, say, outperform an index fund of the S&P 500?

> Second, we conduct the first analysis of members’ portfolio holdings, showing that between 2004 and 2008 the average member of Congress would have earned higher returns in a passive index fund.

https://www.jstor.org/stable/10.1017/s0022381613000194

> For all trades reported electronically and on paper, the buys and sells have the same pattern; they underperform slightly for the first few months and then outperform the market after 150 days by less than 1 percent, which is not statistically significant. Otherwise, the returns of the buys and sells appear to be relatively random.

> The results show that neither Democrat nor Republican senators are especially skilled at picking stocks to buy.

https://home.dartmouth.edu/news/2020/04/us-senators-stock-pi...

Honestly a 100% savings rate isn't terribly hard when all your campaign costs are covered, your travel is covered, your office expenses are covered, and lobbyists or donors pick up the tab on a lot of miscellaneous things. Even assuming zero fraud/abuse/illegality, given that you typically already need to be at least moderately successful financially to run for federal office it's not crazy to think that most members of Congress probably already have paid off cars, paid off or close to paid off homes, etc. Not to mention spouses that probably also have very good paying jobs given the connections you're likely to already have by the time you're running.