The political outlook for President-elect Joseph Bidens first term changed dramatically this week when victory in two Georgia special elections gave Democrats 50 senators. With Vice President-elect Kamala Harris available to decide tie votes, the result means that Democrats will have control of the chamber.

For the first time in a decade, a Democratic Congress will be able to pass laws that a Democratic president can sign. And although Senate Republicans can still wield the filibuster, which requires 60 votes to overcome, Democrats can approve bills through reconciliation , under which legislation can pass the Senate with a simple majority vote.

In principle, Democrats can enact a significant portion of their agenda that way. One reason is that reconciliation is tied to the budget process, and Congress never actually passed a budget last year. The new Congress could take advantage of that by quickly passing a reconciliation bill for the current fiscal year, still leaving opportunities to pass reconciliation bills for fiscal 2022 and 2023.

Thats not even the full extent of legislation Democrats could possibly pass, thanks to an obscure provision of the budget process that seems to allow for revisions to previous reconciliation bills within the same fiscal year.

And it could all happen before the next midterms, when the Republicans will have their first chance to recapture one or both houses of Congress.

But reconciliation is a notoriously cumbersome and complex process, because of interlocking rules on what legislation can and cannot include. And although its possible to alter those rules or challenge interpretations of them, doing so usually requires a series of votes from the full Senate and, in the best of scenarios, the assent of at least 50 senators.

In a practical sense, then, the ultimate limit on what Democrats can do through reconciliation isnt so much process as it is politics specifically, the ability of Democratic leaders like House Speaker Nancy Pelosi (Calif.) and incoming Senate Majority Leader Charles Schumer (N.Y.) to keep their caucuses united.

How Reconciliation Works And How It Has Evolved

Reconciliation dates back to the 1970s, a time when Congress worked a lot differently than it does now. There were two budget resolutions a year, not one, and the original purpose of reconciliation was to adjust revenue or spending bills in order to reconcile them with the overall budget plan.

Part of why the procedures are expedited is because the reconciliation bill was originally imagined to come between the adoption of the second budget resolution, on Sept. 15 and the start of the new fiscal year, on Oct. 1, Molly Reynolds , a senior fellow at the Brookings Institution, explained to HuffPost.

Not long afterward, Congress shifted to one budget resolution a year. But it kept reconciliation as a way to keep revenue and spending in line with the overall budget and to do so quickly, without the risk of delaying tactics like the filibuster.

That opportunity has become a lot more valuable in the past two decades, because of broader changes in American politics and the way they have distorted the lawmaking process. Use of the filibuster has soared ; the two parties have grown more internally homogeneous, geographically and ideologically, making compromise more difficult.