Americans trust their government less and less, according to new polling from Gallup.

Overall, “trust in the three branches of the federal government is collectively lower than at any point in the last two decades,” with those who place a fair amount or great deal of trust in Congress down to 28 percent. At 43 percent, trust in the executive branch has dropped to its lowest point since Watergate. Only the court system fares relatively well, with 61 percent saying they trust the judicial branch.

Overall, trust has been dropping for years. Yes, there have been a handful of spikes—around September 11th, the war in Iraq, and the election of Barack Obama. But each of those hopeful moments was followed by a rapid slide. Here’s Gallup’s graph: 

Gallup PollsGallup Polls

What, exactly, trust represents in a survey like this is somewhat hard to pin down. To some extent it’s just a measure of approval or disapproval, which is why you see a clear partisan split on trust in the executive branch, with 83 percent of Democrats saying they trust the executive, compared to 37 percent of independents and 13 percent of Republicans.

But it’s also a measure of expectation. Will this institution and its members deliver on promises made? Will they act in accordance with the values they claim to hold? Will they make good judgments, and will they act in ways that allow for transparency and accountability?

Which is another way of saying it’s a measure of faith. And on the evidence, Americans have lost a lot of faith in their government—the elected branches in particular.

It’s easy to imagine politicians trying to address this by promising to do everything better, to finally make it all work as promised. That’s sort of what Barack Obama promised back in 2008, when his big idea wasn’t any program or policy so much as a promise to change the way Washington works. Another way of putting this is that he was going to restore trust in the government.

But of course, despite initial hopes, that didn’t really work out, and, in the end, that notion, and its failure, probably contributed overall to the decline in trust: Obama promised big, sweeping cultural changes that were never likely to pay off, and then when they didn’t, trust fell even further. No one likes having their hopes dashed, their expectations shattered.

Which suggests an opening for any politician who is both bold and humble enough to try—acknowledging that there are real limits to what government can accomplish, and promising to do fewer things, but to do them well.