Republicans appeared poised to retain control of the US Senate on Wednesday, after Senator Susan Collins defied political odds to win re-election in Maine and other Republican incumbents led Democrats in a handful of undecided races.

Democrats, who had been favored to win the Senate majority heading into Tuesday’s election, had a net gain of only one seat to show by Wednesday afternoon as their options for further increases dwindled, despite a huge Democratic money advantage going into the final weeks of the campaign.

Republicans currently hold a 53-47 seat Senate majority. To win control, Democrats would need to net three Republican-held seats if Democrat Joe Biden wins the White House and Senator Kamala Harris becomes vice president with the tie-breaking Senate vote.

If Biden loses to Republican President Donald Trump, Democrats would need four seats.

Four Senate races remained undecided by Wednesday evening. Republican incumbents led in three: Alaska, Georgia and North Carolina.

Democratic Senator Gary Peters defeated Republican John James in Michigan, according to projections from television networks and Edison Research.

Senate Majority Leader Mitch McConnell, the top Republican in Congress who won re-election on Tuesday, discussed the possibility of retaining his leadership role at an event in Kentucky, describing his position as “offensive coordinator”.

“If we win in North Carolina [...] I’m still the offensive coordinator,” McConnell said. “I don’t know whether I’m going to be the defensive coordinator or the offensive coordinator as I speak,” he added.

One Senate contest in Georgia was headed for a January 5 runoff between Republican Senator Kelly Loeffler and Democratic challenger Raphael Warnock.

McConnell said a second Senate race on the Georgia ballot, between Republican Senator David Perdue and Democrat Jon Ossoff, could face the same fate.

The best news for Republicans came from Maine where Collins, a Republican moderate once seen as imperiled, pulled off a surprise victory over Democrat Sara Gideon, speaker of the Maine State House of Representatives.

“I feel that this is an affirmation of the work that I’m doing in Washington to fight hard every day for the people of Maine,” Collins told reporters.

Democrats ousted Republican Senators Martha McSally of Arizona and Cory Gardner of Colorado. But those victories were cut to a net gain of one by Democratic Senator Doug Jones’s loss in Alabama.

The Democrats’ path to victory narrowed further as Republican incumbents Joni Ernst of Iowa, Steve Daines of Montana, John Cornyn of Texas and Lindsey Graham of South Carolina — all once viewed as vulnerable — fended off Democratic challengers to win re-election.

Republicans also held onto an open seat in Kansas, where Republican Roger Marshall defeated Democrat Barbara Bollier.

A Republican-run Senate would pose deep problems for Biden if he wins the presidency, likely blocking large parts of his legislative agenda, including expanding healthcare and fighting climate change.

A second Trump term would face a similar hurdle in the House of Representatives, where Democrats held onto a slimmed-down majority.

Close race in Michigan

The Senate race in Michigan drew criticism from Trump just before the contest flipped in the Democrat’s favor and Peters was declared the winner.

“Wow! It looks like Michigan has now found the ballots necessary to keep a wonderful young man, John James, out of the US Senate. What a terrible thing is happening!” Trump wrote on Twitter.

In North Carolina, Republican Senator Thom Tillis declared victory over his Democratic challenger, Cal Cunningham.

The race had not been called, with Tillis leading by less than two percentage points. State election officials said no further results would be available until November 12 at the earliest, when all mail-in ballots are received and counted.

In Georgia, Perdue was more than three percentage points ahead of Democrat Jon Ossoff in Georgia.