(Reuters) - U.S. Senate control hung in the balance while Republicans edged closer to securing a majority in the House of Representatives on Wednesday, a day after Democrats outperformed expectations and avoided a Republican "red wave" in midterm elections.
The Senate contests in Nevada and Arizona, where Democratic incumbents were seeking to hold off Republican challengers, were as yet undecided, with thousands of uncounted ballots that could take days to tally.
If the parties split those races, the Senate's fate would come down to a Georgia runoff election for the second time in two years, after Edison Research projected neither Democratic incumbent Raphael Warnock nor Republican Herschel Walker would reach the 50% necessary to avoid a Dec. 6 one-on-one rematch.
Republicans were closing in on the 218 seats needed to wrest control of the House from Democrats, with 210 now in their column, Edison Research projected. But 21 of the 53 most competitive races, based on a Reuters analysis of the leading nonpartisan forecasters, were still pending as of Wednesday evening, raising the prospect that the final outcome may not be known for some time.
Even a slim House majority would let Republicans hem in Democratic President Joe Biden during his next two years in office, blocking legislation and launching potentially politically damaging investigations.
Speaking at a White House news conference, Biden vowed to work with Republicans and said he understood voters are frustrated despite Democrats' surprisingly competitive campaign.
"The American people have made clear, I think, that they expect Republicans to be prepared to work with me as well," Biden said. He also reiterated his intention to run for re-election in 2024 and said he would make a final decision early next year.
A White House official said Biden spoke by phone on Wednesday with Republican House leader Kevin McCarthy, who would be the leading candidate for House speaker if Republicans win a majority.
The election fell short of the sweeping victory Republicans had sought, as Democrats eluded the kind of heavy midterm defeat that often plagues sitting presidents of either party.
The results suggested voters were punishing Biden for presiding over an economy hit by the steepest inflation in 40 years at 8.2 percent, while also lashing out against Republican efforts to ban abortion and cast doubt on the nation's vote-counting process.
Poor performances by some candidates backed by Donald Trump - including Walker - signaled exhaustion with the kind of chaos fomented by the Republican former president, raising questions about the viability of his possible 2024 White House run.
"I think his ego is just too big to handle," said Yvonne Langdon, 75, as she cast her ballot for Republican candidates in Michigan on Tuesday.
Biden had framed Tuesday's election as a test of U.S. democracy at a time when hundreds of Republican candidates embraced Trump's false claims that the 2020 presidential election was stolen.
A number of election deniers who backed Trump's claims were elected to office on Tuesday, but many of those who sought positions to oversee elections at the state level were defeated.
"It was a good day, I think, for democracy," Biden said.
Fears of violence or disruption by far-right poll watchers at voting stations did not materialize. Jen Easterly, head of the U.S. Cybersecurity and Infrastructure Security Agency, said she saw no evidence any voting system was compromised.