Election workers process ballots at the Maricopa County Tabulation and Election Center on Thursday in Phoenix. Over 100,000 ballots were left to still count after the midterm election Tuesday. Joshua Lott/The Washington Post

Outstanding ballots in two states and a runoff election in a third have left control of the Senate up in the air, with Arizona and Nevada racing to count votes on Thursday and rival candidates in Georgia gearing up for another four weeks of campaigning.

Democrats were cautiously optimistic Sen. Mark Kelly’s lead would hold in Arizona and in Nevada, where Sen. Catherine Cortez Masto is trailing, they think that mail ballots from urban areas will help catch them up. Some Republicans privately agreed their candidates could lose, but others in the GOP expressed confidence that Blake Masters would pull through in Arizona and Adam Laxalt would stay ahead in Nevada.

Democratic incumbents need to win at least two of the three states to retain power. Even if the Republicans ultimately become the majority in the House, continued Democratic control of the Senate would preserve President Biden’s ability to have his judicial nominees and administration appointments confirmed.

Officials in neither Arizona nor Nevada expect to finish counting before the weekend. Meanwhile money has begun to pour into Georgia for a Dec. 6 runoff race that could determine the Senate majority. Neither Democratic Sen. Raphael Warnock nor Republican Herschel Walker received more than 50 percent of the vote required to win outright.

As of Thursday afternoon, the Arizona secretary of state’s office estimated that more than 600,000 ballots remained to be counted statewide. Officials in Maricopa County – where roughly 400,000 votes had yet to be counted – said a full tally could take several more days. In Nevada, more than 50,000 ballots have yet to be counted with more arriving daily in the mail – they can be received as late as Saturday – and over 7,000 ballots need to be cured.

That Arizona and Nevada’s races have yet to be called is not surprising – the narrow margins in many contests means it takes longer to project a winner, and they have many mail-in votes to process.

Maricopa County, Arizona’s biggest battleground, saw more than 275,000 early ballots dropped off on Election Day – about 100,000 more than in 2020, according to Maricopa County Recorder Stephen Richer (R).

Both Democrats and Republicans in the state anxiously awaited updates from election officials, as strategists watched to see how a surge in Election Day ballot drop-offs would move the numbers in the race. Kelly is leading Masters by five percentage points, with a little more than 70 percent of the ballots counted.

Maricopa County election workers process ballots in Phoenix. Joshua Lott/The Washington Post

Both parties expect the mail ballots dropped off on Election Day to tighten the race, but it’s not clear exactly how they will break. So far Republicans have done better with Election Day votes than they have mail-in votes, a reflection of growing distrust in Arizona’s well-established mail voting system driven by former president Trump’s false claims that the process was fraudulent.

“We continue to be confident that we will win this race, and are grateful for Arizona’s elections officials working around the clock to count outstanding ballots across the state,” said Emma Brown, Kelly’s campaign manager.

Masters’ campaign expressed confidence that he can close the gap with Kelly, but some national strategists from both parties are skeptical based on the margins they’ve seen so far and believe Kelly will win.

The Election Day drop-off ballots breakdown “will either keep Blake’s hope alive or allow Kelly to breathe easy,” said Arizona GOP strategist Barrett Marson.

Masters suggested on Tuesday that something nefarious was occurring but fell silent on social media as Kelly gained an edge over him in incomplete results. A fundraising appeal from Masters’s campaign on Thursday did not allege impropriety but argued that “some of the issues we’ve see occur during this election are troubling.” It added, “We’re expecting a contested road forward and legal battles to come.”

Maricopa County election workers Joshua Lott/The Washington Post

Not only is Masters trailing Kelly, he’s also lagging a few points behind Republican gubernatorial candidate Kari Lake, who appears to have a better chance of winning when all the votes are counted. A Libertarian candidate who endorsed Masters late in the race has garnered 2 percent of the vote for Senate.

In Nevada, national Republicans feel more optimistic, as a smaller number of ballots remain to be counted with Laxalt in the lead by about 16,000 votes as of Thursday afternoon. Democrats believe that the remaining mail-in ballots will skew in Cortez Masto’s favor.

Republican strategists hoped some of those outstanding mail ballots would prove more favorable for them, betting that, as in Arizona, GOP voters’ distrust of the mail voting system improves their margins with Election Day drop-offs. But Democrats note the remaining votes include drop box ballots – a method that some Republicans distrust.

Recent batches of the remaining mail votes have shown Cortez Masto gaining the margins she needs to overtake Laxalt, and some GOP strategists said privately Thursday that Laxalt could struggle to keep his lead.

Laxalt disagrees. “We expected the remaining mail universe to fall well below the percentage (Cortez Masto) needs to catch us,” he tweeted Thursday morning. “No status change.”

Sen. Raphael Warnock (D-Ga.) delivers remarks to supporters and attendees at the John Lewis Mural in Atlanta on Thursday. Demetrius Freeman/The Washington Post

Also Thursday, former president Donald Trump attempted to sow doubt with baseless claims about the counting process in both states.

“Clark County, Nevada, has a corrupt voting system (be careful Adam!), as do many places in our soon to be Third World Country. Arizona even said ‘by the end of the week!’ – They want more time to cheat! Kari Lake MUST win!” Trump posted on TruthSocial.

Joe Gloria, Clark County registrar of voters, on Thursday refuted accusations of corruption in the county’s election process.

“Obviously he’s misinformed, two years later, about the law and our election process,” Gloria said. “We couldn’t go any faster now even if we wanted to. We’re working as hard as we possibly can.”

All was quiet outside the election headquarters on the northern edge of Las Vegas on Thursday, as more than 200 workers sorted and counted ballots behind closed doors and under police guard. So far, few seem interested in following Trump’s lead questioning the results, and there no protests outside the counting facility as there were two years ago. Even Jim Marchant, a candidate for secretary of state and a prominent 2020 election denier nationally, has not weighed in on the Clark County process as the nation waits for Nevada’s results. That race also is too early to call.

In Georgia, both Republicans and Democrats are preparing for an expensive runoff just as their donor and activist base are exhausted from a grueling midterm cycle. One Republican strategist said Trump announcing his presidential run before the Dec. 6 runoff would not be helpful, since it would distract from a message they are hoping to keep focused on inflation, border security and crime.

After a hard-fought campaign, Warnock and his Republican challenger Walker jumped right back into campaign mode.

Warnock on Thursday offered remarks in front of a downtown Atlanta mural honoring the late civil rights icon, Rep. John Lewis (D-Ga.), and joked to supporters that he had warned them they might be spending Thanksgiving together. Warnock, who won a runoff election to become Georgia’s first Black senator less than two years ago, was welcomed by a large crowd of supporters, who held up signs that read “One more time Georgia.”

“Now, we all knew this election would be close – but I’ve done this before. We’ve done this before. We know how to win a runoff,” Warnock said as supporters cheered him on. “Now, that doesn’t mean it’s going to be easy.”

“They’re going to throw every dollar at us that they can. Every lie, every attack,” the Georgia Democrat added. “But I think we have something better: We have the truth. We have hope for the future.”

National leaders and surrogates on both sides of the aisle are expected to descend upon Georgia over the next four weeks. Leading up to Tuesday’s election, however, it was national Republicans who were flocking to the battleground state to rally around the former football star, whose campaign was rocked by allegations of domestic violence, that he failed to support some of his out-of-wedlock children and that he paid for two former girlfriends to have abortions.

Walker was set to launch an “Evict Warnock” bus tour on Thursday evening, hosting an event in Canton, Ga., a small city just north of Atlanta, with Sen. Ted Cruz (R-Texas). Walker’s bus tour leading up to Tuesday’s election was called the “Unite Georgia” bus tour.

Democratic and Republican groups, meanwhile, have readied to pump millions into the race.

The Democratic Senatorial Campaign Committee on Thursday announced it would spend $7 million on field operations in the Georgia Senate runoff. The money will fund direct voter contact programs, namely door-to-door canvassing, the DSCC said.

Georgians also won’t get a reprieve from campaign advertising. The National Republican Senatorial Committee on Thursday reserved $234,000 for television ads, marking the first spending of the runoff, according to AdImpact, which tracks television and digital ad spending.