Democrats Didn’t Just Win Georgia. They Secured a Firmer Grip on the Senate.

WASHINGTON — Senator Raphael Warnock’s victory in Georgia’s runoff election on Tuesday delivered Democrats just one additional seat, but that single layer of padding for their majority will hand them exponentially more leeway to control the chamber than they have now.

Mr. Warnock’s success gives Democrats a 51-to-49 majority in the Senate beginning in January, expanding the bare minimum hold they currently have by virtue of Vice President Kamala Harris’s tiebreaking power in the evenly divided chamber.

The implications for Senate Democrats and the Biden administration extend well beyond the single Senate slot. With an additional vote, Democrats can take much more operational control of the Senate, easing the confirmation of contentious nominees, clearing the way for investigations and in general availing themselves of breathing room on a variety of matters.

“It makes all the difference in the world,” said Senator Richard J. Durbin of Illinois, the No. 2 Senate Democrat and chairman of the Judiciary Committee, which would find its work filling judicial vacancies to be much less fraught with a bigger majority.

A larger Democratic contingent will give the party a one-seat advantage on congressional committees that are now evenly split, a situation that allows minority Republicans to maintain significant leverage over legislation and other business. As a result, some administration nominees have stalled in committee, while others have made it out only through a special floor procedure that costs Democrats time. Having an edge on the committees will allow Democrats to overcome Republican opposition, if they can hold together.

“It is good for the efficiency of the Senate,” said Senator Sherrod Brown, Democrat of Ohio and chairman of the Banking Committee, where united Republican opposition held up some of President Biden’s nominees for a time this year. “We can be more nimble, we will be a lot quicker, we will be a little more decisive and that’s good. It doesn’t mean we will pass everything.”

An enlarged majority also dilutes the influence of individual senators such as Joe Manchin III, Democrat of West Virginia, who has used his swing-vote status to exert significant control over legislation and helped derail some of the main elements of Mr. Biden’s agenda. Mr. Manchin, however, has said that he would welcome a wider margin because it would take some of the attention and pressure off him as he weighs another run in 2024.

Such a situation would “make it easier for me,” Mr. Manchin told reporters last week on Capitol Hill.

Mr. Warnock’s win also secured for Democrats the authority to subpoena witnesses before Senate committees without the cooperation of Republicans, which could be hard to come by if the G.O.P. disagrees with the subject of the inquiry or views it as partisan. With House Republicans planning an onslaught of investigations when they assume control in January, the ability of Senate Democrats to mount their own investigations could allow them to counterpunch.

“The subpoena power is going to be very important, especially as the House goes into overdrive on investigations,” said Senator Chris Van Hollen, Democrat of Maryland. “It will provide some check and balance.”

Had Mr. Warnock lost, Democrats still would have retained control of the Senate, but under the existing 50-50 setup, with its attendant hurdles. That outcome would have doubtless been deflating to Democrats considering how eagerly they have looked forward to a 51-to-49 split after two years of struggling with evenly divided numbers.

Republicans knew what was at stake as well, and Mr. Walker sought to make it an issue even after Democrats clinched the Senate majority last month with the victory of Senator Catherine Cortez Masto in Nevada.

“If I lose this runoff, Democrats will have a 51-seat majority where the most radical proposals will succeed,” a fund-raising appeal from Mr. Walker said. “We cannot let that happen.”

Republicans said they were sorry to see their power diminished in the Senate, but noted that the narrow Republican majority in the House would deprive Democrats of the ability they now have to control both chambers and use a special budget procedure known as reconciliation to roll over Republicans on tax and spending issues, as they did twice in the past two years.

“I’d much rather have 50-50 than 49-51,” acknowledged Senator John Cornyn, Republican of Texas, who noted that the new House majority would be a backstop against reconciliation. “I think the voters kind of like the idea of us being stalemated. Either bad things won’t happen, or if things do happen, it will have to be the old-fashioned way by finding consensus.”

But Democrats were thrilled about their new numbers, impatient for an expanded majority after two years of the longest evenly divided Senate in history.

In a body that has experienced frequent absences due to the coronavirus and other medical conditions, the added seat will make everyday scheduling a little less difficult, relieving Democratic leaders of the need to make sure that every senator is on hand for close votes, and sparing Ms. Harris the chore of idling nearby in the event she is needed.

The 51st seat also means that Democrats will have an added boost heading in 2024, no small matter when they will be defending seats in Republican-leaning states such as West Virginia, Montana and Ohio.

There are other, less tangible, benefits as well, after Democrats who were widely anticipated to lose a seat or two instead gained one and tightened their grip on the Senate.

“It gives Democrats in the Senate a kind of bounce in our step that we can build on,” said Senator Ron Wyden, Democrat of Oregon and the chairman of the Finance Committee.