Congress returns next week to face a long Senate slog on immigration, a farm bill competing for the House’s attention with going-nowhere-fast abortion restrictions and the lowest level of public confidence Gallup has ever recorded for a bedrock American institution.

The firm’s latest numbers about Congress were pretty much overlooked when they were released this week because, at first blush, the figures seemed only to echo the recent spate of abysmal congressional approval ratings.

But the new poll suggests something more worrisome about the workings of our democratic society. Whether the people are confident the legislative branch is functioning properly, an admittedly vague concept, sounds like a more reliable gauge of the institution’s long-term viability than whether they like what’s being served up at the Capitol at the moment.

That might help explain why Gallup has been asking the confidence question just once a year for four decades but gauges congressional approval every month.

In the first four days of June, only 10 percent of 1,529 people surveyed described themselves as having a great deal or quite a lot of confidence in Congress, ranking it last on a list of 16 societal institutions for the fourth consecutive year. No institution has scored lower since Gallup started asking in 1973.

The faith-in-Congress figure is one-third what it was a decade ago. And it’s slipped 3 points in a year. (During that time, the monthly approval ratings taken by the Gallup and New York Times-CBS polls have averaged 15 percent.)

The measure of confidence the public has in its lawmakers is a tiny fraction compared to the figures for some of the institutions the government pays for and regulates.

The military is tops in the new Gallup survey at 76 percent, followed by small business at 65 percent. Confidence in the medical system was 35 percent, down 6 points in the year since Obamacare began taking effect, while confidence in banks spurted up 5 points, to 26 percent in a sign of easing economic worry. Even the institutions near the bottom — organized labor, big business and HMOs — had numbers twice as high as Congress.

Underscoring the crisis of confidence, Congress was the only institution this year in which a majority expressed very little or no faith at all. The number was 52 percent; television news was the institution with the next most-pronounced lack of confidence, at 39 percent.

The numbers are also sobering for lawmakers holding out hope they might harness public perception at this summer’s crucial junction for the 113th Congress. President Barack Obama and the Hill are nearing a turning point on his second-term legislative program, and the Supreme Court could insert itself forcefully into the legislative debate with its impending rulings on collegiate affirmative action, gay marriage and the Voting Rights Act.

Confidence in the other two branches have slipped a bit in the past year, as well, but the figures for both the presidency (36 percent) and the high court (34 percent) are still more than triple that of Congress.

In contrast to the old truism about polling about Congress — voters may hate it, but they love their congressman and are OK with the leaders of the party they support — the current paucity of confidence in Capitol Hill is equivalent among Democrats, Republicans and independents.

And that’s a switch from the past, which suggests voters have become noticeably rattled and frustrated by the divided government they say they want and have voted for in the past two elections.

Four years ago, when Obama began advancing his agenda with the help of then-Speaker Nancy Pelosi, D-Calif., and Senate Majority Leader Harry Reid, D-Nev., Democratic confidence in Congress was 27 percent — 17 points higher than the GOP figure. Three years earlier, when J. Dennis Hastert, R-Ill., and Bill Frist, R-Tenn., were the top Hill promoters of George W. Bush’s agenda, Republican confidence in Congress was 27 percent — 14 points higher than the faith Democrats expressed. But since divided government returned in 2011, the figures have always been within a handful of points of each another.

Congress has not enjoyed a stronger vote of confidence than the 42 percent it achieved the first time Gallup took the measure, in 1973. That may be an unfair benchmark to set for the current institution. This season’s glib comparisons between Obama and Richard Nixon aside, that year saw an extraordinarily self-confident Congress best the president in a high-profile battle over the power of the purse before turning its spotlight on the campaign finance and criminal implications of Watergate.

It’s also true bedrock American institutions did generally better back then; organized religion topped the list at 66 percent, followed by the public education system at 58 percent.

This year, confidence in the church is down by one-quarter from that benchmark, faith in schools is off by half. And confidence in Congress is down by three-quarters.

It has hardly anywhere to go but up. It may take another fiscal or constitutional crisis to turn it in that direction.