Three weeks into the government shutdown, Washington, D.C., restaurants are trying to brighten the mood—and shore up business—with gimmicks like free croissants or specialty cocktails named “Furlough-rita.” One place, Barrel, on Pennsylvania Avenue, has tried to lure in customers with an “Unhappy Hour.”

But there’s no sugarcoating it: By Wednesday, this shutdown will be the second-longest ever, beating the 21-day affair Republican House Speaker Newt Gingrich triggered during the Clinton administration. And it shows every sign of exceeding the 35-day record set during the first Trump administration.

The policy issues at stake are complicated. The reason it’s dragging on, however, is perfectly simple and easily summarized in that age-old nostrum: “Incentives influence behavior.”

Republicans and Democrats in Congress had strong incentives to let the shutdown happen, and both have strong incentives to keep it going.