The eyes of the political world remained focused on Arizona and Nevada on Friday, where hundreds of thousands of uncounted votes held the key to control of the US Senate, three days after Americans cast their final ballots in midterm elections.

The delay in districts such as Arizona’s Maricopa county, which includes Phoenix, is attributed to the record number of ballots cast on Tuesday. Election officials had estimated they would have a tally by Friday but now say they will count through the weekend.

In Nevada, election officials had estimated a finish by Friday but, again, the high number of ballots cast means counting will continue through next week. However, a winner could be called as soon as any candidate is judged to have passed a majority threshold.

If Democrats or Republicans can capture a majority by sweeping the contests in both states, it will settle control of the Senate. A split, however, would transform a 6 December runoff Senate election in Georgia between incumbent Democratic senator Raphael Warnock and Republican Herschel Walker into a proxy battle for the chamber, which among other powers holds sway over Joe Biden’s judicial appointments.

Meanwhile, Republicans were slowly inching closer to wresting control of the House of Representatives from Biden’s Democrats, which would in effect give them veto power over his legislative agenda, allow them to launch investigations into his administration and have greater control over the budget.

Biden conceded on Thursday that Democrats face long odds to keep control of the House.

“It’s still alive. It’s still alive. But it’s like drawing an inside straight,” Biden said, using a poker term for an unpromising situation.

Biden said he had spoken to the House minority leader, Kevin McCarthy, a day earlier, after an upbeat press conference at the White House.

“I said: ‘If you win the majority, congratulations,’” Biden recalled, in a fine distinction after McCarthy told Fox News that the president had congratulated him on winning a majority.

Republicans had secured at least 211 of the 218 House seats they need for a majority, Edison Research projected late on Thursday, while Democrats had won 197. That left 27 races yet to be determined, including a number of close contests.

The Republican House leader, Kevin McCarthy, has already announced his intention to run for speaker if Republicans win, an outcome he described as inevitable on Wednesday.

But his path could be blocked by a handful of conservative Republicans known as the Freedom Caucus. McCarthy needs 218 votes, so fewer than a dozen caucus members have power to block his path.

“No one currently has 218” votes, Chip Roy of Texas told NBC News as he emerged from a private Freedom Caucus meeting.

Tuesday’s results fell far short of the sweeping “red wave” that Republicans had expected, despite Biden’s anaemic approval ratings and deep voter frustration over inflation.

Democrats portrayed Republicans as extremist, pointing to the supreme court’s decision to eliminate a nationwide right to abortion and the hundreds of Republican nominees who promoted former president Donald Trump’s false claims that the 2020 election was fraudulent.

Some of Trump’s most high-profile endorsed candidates lost pivotal races on Tuesday, marring his status as Republican kingmaker and leading several Republicans to blame his divisive brand for the party’s disappointing performance.

The outcome may increase the chances that the Florida governor, Ron DeSantis, who routed his Democratic challenger on Tuesday, opts to run for the 2024 presidential nomination. While Trump has not officially launched a third White House campaign, the former president has strongly suggested he will do so and has said he will make a “special announcement” at his Florida club on Tuesday.

Trump lambasted DeSantis in a statement on Thursday, taking credit for the governor’s political rise, while attacking critics on his social media site, Truth Social.

Even a narrow Republican House majority would be able to demand concessions in exchange for votes on key issue such as raising the nation’s borrowing limit. But with few votes to spare, McCarthy might struggle to hold his caucus together – particularly the hard-right faction that is largely aligned with Trump and has little interest in compromise.