OVER the 40 years preceding Barack Obama’s first term in office, under Republican and Democratic presidents alike, the federal government claimed, on average, about 18 percent of America’s gross domestic product in taxes every year and spent slightly under 21 percent.

This equilibrium was always going to be threatened by the retirement of the baby boomers. But the financial crash and the Great Recession upset it sooner than anyone expected. As the economy cratered, so did tax revenue, dropping below 15 percent of G.D.P. in 2009. Government spending, meanwhile, climbed to 25 percent of G.D.P., as the president’s stimulus bill tried to help fill the gap left by the private sector’s collapse.

This gulf between taxes and spending has closed, somewhat, in the three years since, thanks to the limping recovery and some halting attempts at deficit reduction in Washington. But a new equilibrium will take many more years of growth and many more painful policy decisions to achieve.

The choice voters face on Tuesday will not determine exactly where this new equilibrium ends up. An Obama second term and a Romney first term would both feature a certain amount of can-kicking and a certain amount of compromise. A President Obama would probably accede to further spending cuts; a President Romney would likely accept the need for slightly higher tax revenue. Both men would continue to run large deficits as long as the recovery seemed weak.