Sen. Chuck Schumer (D-N.Y.) made headlines Sunday morning by promising that Senate Democrats will write and pass a full tax and spending bill by the March 1 deadline for the next budget. "It’s going to be a great opportunity for us because in our budget that we will pass, we will have tax reform, which many of my Republican colleagues like. But it’s going to include revenues," Schumer said on "Meet The Press."

The pledge by Schumer, the Senate's third-ranking Democrat, indicates that Democrats are willing to go along with the proposal that House Republicans made at the end of their retreat last week: They'll extend the debt ceiling without upfront spending cuts for three months, so long as the Senate passes a budget blueprint this spring.

But such negotiations may raise a fairly obvious question: Why is the very act of passing a budget a point of contention in the first place? Isn't this what Congress should be doing in the first place?

Technically, the 2011 debt-ceiling deal already set the discretionary spending levels for the next 10 years, which includes nearly $1 trillion in discretionary cuts that have already begun to take effect. But, as the New York Times points out, Congress can still vote to change the 2011 caps. And by agreeing to pass a new budget—one that will presumably replace the sequester's $1.2 trillion in cuts through entitlement and revenue changes as well as discretionary cuts—both Democrats and Republicans have agreed to revisit the budget through a traditional budget resolution process that's been stymied for the past four years.*

Traditionally, the budget rarely passes on schedule, but the process has broken down more dramatically as political polarization and angst over spending has surged on Capitol Hill. As I've reported before, Congress has enacted a full set of spending bills by the annual deadline only four times in 30 years (1977, 1989, 1995 and 1997), relying instead on temporary spending bills and omnibus bills to keep the government running.

Before Congress and the president even get to enacting appropriation bills, however, Congress needs to pass a budget resolution—the blueprint for spending that's further delineated in the individual appropriations bills. In fact, the Senate hasn't passed a budget resolution since April 2009, and even then, the tax and spending legislation didn't receive a single Republican vote in Congress.

Since the GOP won back the House, Senate Majority Leader Harry Reid (D-Nev.) has held back from writing a full budget blueprint: Democrats have instead resorted solely on omnibus appropriations and continuing resolutions to keep the government going, thwarting the GOP's ability to offer amendments to cut spending or put political pressure on Democrats. "The party in the minority has traditionally used the budget debate to score political points with amendments that mean little but are intended to put senators on record on contentious political issues," Jonathan Weisman explains.

Republicans have turned the Senate's inaction on a budget resolution into a major talking point. ("1,361 Days Since Senate Passed a Budget," Speaker Boehner's (R-Ohio) office declared Friday.) But the budgeting process has also slowed down in part because of the very reforms that House Republicans instituted in 2010 to clean up the way that Washington deals with spending. When House Republicans came to power, they passed a ban on earmarks, which have traditionally greased the wheels of budgeting. BusinessWeek explains what's happened as a result:

Since the ban took effect, the appropriations process has “melted down,” says Sean Kelly, a professor at California State University Channel Islands... In dozens of conversations with staffers and members of Congress, he’s found that there’s now less incentive for a politician to serve on an appropriations committee because there’s nothing to hand out. As a result, says Kelly, the committees attract more partisans and fewer pragmatists–to its detriment. “There’s a human element in lawmaking that is real,” says Tom Cole, a six-term House Republican from Oklahoma. Without earmarks, “you’re removing all incentive for people to vote for things that are tough.”

In the next few months, Senate Democrats will take steps to ensure that they'll pass a full budget resolution: Schumer's spokesman tweeted that Democrats will use the budget reconciliation process to fast-track the reach a deficit deal, which allows the Senate to pass it with 51 votes and avoid a potential filibuster. But that also means that the bill will be strictly limited to provisions that have a major fiscal impact, limiting outside horse-trading as well.

*Post has been updated to explain how the 2011 debt-ceiling deal affects the current budget negotiations, and to clarify the difference between a budget resolution and individual appropriations bills.