Even before this new record high, in the previous ~15 years the average seemed to be around 75% (±), which seems… high? I would perhaps understand the US public thinking that (some levels of) government being "incompetent", but not corrupt.

By some measure the US does seem to have 'decent' scores for perception of corruption:

* https://en.wikipedia.org/wiki/Corruption_Perceptions_Index

* https://www.transparency.org/en/cpi/2025

Meta: in some ways it seems that the public's perception of government is a bit of a self-fulfilling prophecy. In the US there is a large vein of "government is bad/incompetent/corrupt" and that's apparently what the US often gets. While in (e.g.) Scandinavian countries there appears to be a higher level of trust in government, and the people there tend to elect more competent politicians (?).

I imagine having over a dozen political parties helps with this as well.

I'd guess it comes down to what counts as "the government."

Millions of people work for the federal government, and millions more for state and local governments. Is there widespread corruption among them? I don't think so. And I don't think my countrymen think so either.

But "the government" is often meant as just the very top. The President is corrupt. Big swathes of Congress are corrupt. We have a Supreme Court justice more or less openly accepting bribes. Among that small group, I would be comfortable saying that corruption is widespread.

This is what a steady diet of conservative, increasingly monopolistic, media does to a populace.