HAVE THE NATION’S LEADERS ever seemed smaller? It’s hard to remember when.

Unable to do what they all understood needed to be done, they created last year a congressional “supercommittee” that was meant to function as Congress had ceased to function. To guarantee its success, they established a fail-safe mechanism: a series of spending cuts that would take effect in event of failure that were so onerous that no patriot could contemplate their realization.

The supercommittee failed in the fall of 2011. Congress and President Obama essentially took the next year off to run for reelection. And then, as the fail-safe mechanism loomed, and scheduled tax increases threatened to send the nation reeling back into recession, the leaders failed to rise to the moment they had created for themselves. Instead of crafting a bargain that could set the nation on a steadier fiscal course, they jockeyed to ensure that their political opponents would bear the public ire when things went sour. That’s how small politicians behave.

We understand that the two parties have starkly different understandings of the role government should play in U.S. society. They’ve been fighting to defend those visions, and they will continue to do so. That’s as it should be.

Meanwhile, interest groups on both sides create a toxic environment for politicians who understand that compromise also will be needed. Whether it’s the no-tax puritans on the right or the hands-off-entitlements zealots on the left, the groups thrive in an atmosphere of maximum confrontation. Over time they help elect politicians who share their purity of vision — who believe that compromise is a betrayal of the voters who sent them to Washington.

But for reasons substantive and political, compromise will be essential. As the population ages and health-care costs soar, two things need to happen if the nation is not to sink into debilitating debt: revenues have to rise, and spending — especially on Medicare, Medicaid, Social Security and military health care — has to be brought under control. And with the nation evenly divided between red and blue, a division expressed in the shared power in Congress, no solution that pleases the puritans has a chance of becoming law.

Speaker John Boehner and Senate Minority Leader Mitch McConnell, wily Republican survivors, understand this reality perfectly well, even if not everyone in their caucuses does. They know that Congress will never fashion the small government of Republican dreams, one that lives on 18 percent of GDP, because in the end that is not the government Americans want. But they refuse to acknowledge forthrightly the responsibility to pay for the larger government of reality.

Mr. Obama likewise understands that the entitlement programs cannot continue on their path of perpetual growth. Yet since the election he has remained in campaign mode, pretending that the problem can be solved mostly by raising taxes on the rich. When he grudgingly agrees to a relatively small adjustment on the spending side — to the manner in which Social Security cost-of-living adjustments are calculated, for example — it is presented as a “concession.” But why is it something he has to concede, when such adjustments and many more are plainly in the national interest? Why is the nation’s leader not embracing and then explaining the balanced reforms the nation needs?

As we write, it’s not clear whether Mr. Obama and Congress will salvage some small deal out of their embarrassing last-minute wrangling or whether the nation will fall off the fiscal cliff. We hope it’s the former — but a last-minute fix would have little effect on the debt. Either way, our politicians will have managed only to postpone many of the tough decisions while sharpening questions around the world about America’s fitness as a global leader and exemplar.