WASHINGTON — The titanic struggle over how to reach a broad Congressional tax agreement is not just the latest partisan showdown, but rather the culmination of two years of escalating fiscal confrontations, each building on the other in its gravity and consequences. On Sunday, lawmakers could not seem to find one final way out.

From the first fight over a short-term spending agreement to keep the government open in early 2011 to the later tangle over the debt ceiling to the failure of last year’s special budget committee and the resulting automatic spending cuts that now loom along with tax increases, the so-called fiscal cliff was built, slab by partisan slab, to where it now threatens the nation’s finances.

“Something has gone terribly wrong,” said Senator Joe Manchin III, Democrat of West Virginia, “when the biggest threat to our American economy is the American Congress.”

Years of increased spending on everything from wars to expanded entitlement programs — combined with protracted, stubborn unemployment and a nation of workers whose earning power and home values have plummeted in recent years — have persuaded lawmakers in both parties that fiscal policy is the most pressing domestic concern.