The U.S. Senate has a gang problem. To tackle immigration, senators formed a Gang of 12. On energy policy, they tried a Gang of 10 (which became a Gang of 20). Now, under pressure to lower the national debt, Congress is waiting for a bipartisan plan from a Gang of Six.

Those are the gangs. This is the problem: Often, they don’t work.

The gangs of 12, 10 and 20 all failed. So did the Senate’s last Gang of Six, which sought bipartisan agreement on health care in 2009. These informal groups are intended to create breakthroughs, in a Senate paralyzed by odd rules and polarized parties. But they usually fizzle out, because the Senate is paralyzed by odd rules and polarized parties.

Last week, the newest gang was already dragging its feet. So the Senate may be on the verge of re-learning a lesson that it never seems to remember.

“It’s soothing to believe that these seemingly intractable problems can be at least addressed by people of goodwill, working together” in gangs, said Ross Baker, a professor of political science at Rutgers University. “Even though they can’t be,” he said.

The current Gang of Six — three Republicans and three Democrats — has been working together for months. Its goal is to forge a compromise on the most divisive issue in today’s Congress: how to reduce the deficit and the ballooning national debt.

Gangs such as this one are a product of the Senate’s independent ethos. The House functions like two choirs: party leaders pick the music, and their members generally line up and sing. The Senate, on the other hand, acts more like 100 soloists, each feeling free to make his own alliances.

A “gang” is usually an alliance focused on a specific issue, which forms outside the Senate’s party structures. The media nickname for these groups is new, taken from the “Gang of Four” that helped rule China in the 1960s and 1970s.