Nancy Pelosi has been narrowly re-elected Speaker of the US House of Representatives, with a new Congress taking office amid political uncertainty.
The House voted 216-209 to reinstate Ms Pelosi on Sunday (local time), after Democrats lost 11 seats in the November elections to command a narrower 222-212 majority.
Five Democrats chose not to support her - two voted for candidates not running, while three others simply voted "present".
The Senate remains Republican-run ahead of twin elections in Georgia on Tuesday, giving its members a platform to again air President Donald Trump's baseless claims his loss to Joe Biden was fraudulent.
Multiple state and federal reviews have found no evidence to support the claims but Republican senators and House members plan to challenge the election result when Congress certifies it on Wednesday.
A push led by Senator Ted Cruz for an emergency 10-day audit of results in contested battleground states drew criticism on Sunday from staunch Trump ally Lindsey Graham.
"It appears to be more of a political dodge than an effective remedy," he said.
"I will listen closely but they have a high bar to clear."
The narrower balance of power in both chambers could also encourage moderates from each party to flex their muscles, especially after Trump leaves the White House on 20 January and Mr Biden takes office.
But leaders in both the House and Senate tried to sound optimistic despite mounting challenges.
"From political division to a deadly pandemic to adversaries around the world, the hurdles before us are many and serious," Senate Majority Leader Mitch McConnell said on the Senate floor.
"But there is also plenty of reason for hope," the Kentucky Republican added, citing the ongoing rollout of coronavirus vaccine.
"I'd say 2021 looks bright already."
House Majority Leader Steny Hoyer, the chamber's No. 2 Democrat, also said he hoped the new Congress would "turn the page" on partisan division "and begin a new chapter of co-operation."
A smaller Democratic majority and the still-raging coronavirus pandemic made re-election as Speaker trickier for Ms Pelosi, the only woman ever to hold job.
The smaller caucus meant less room for dissident Democrats to vote against her without risking a possible win for Republican Kevin McCarthy, who opposed her.
"It's not personal. It's not malicious. It just represents a feeling in my district," Democratic Representative Elissa Slotkin of Michigan told reporters before voting "present".
"We need a different crop (of leaders) that represents a broader swath of the country," Ms Slotkin said.
In the Senate, Vice President Mike Pence swore in 32 senators on Sunday, administering the oath of office in pairs due to COVID-19 restrictions.
Senator John Hickenlooper greets Vice President Mike Pence as he takes the oath of office during a ceremony in Washington, DC, 3 January 2021. Source: AAP
A Republican win of one or both Georgia Senate seats up for election on Tuesday would cement the Republican majority led by McConnell.
Twin Democratic wins in Georgia would produce a 50-50 Senate, where Democratic Vice President-elect Kamala Harris would hold the tie-breaking.
