And while voters in the Grand Canyon state are used to having their election results take a little longer -- because of signature verification used on ballots sent in by mail -- the delay has dragged on.
“Usually the results are known by the Friday or Saturday after the election,” said Richard Herrera, a political science professor from Arizona State University.
“This is taking a long time because, first of all, the history of Arizona state-wide elections is one in which Republicans usually win handily so there just haven’t been that many close state-wide races and high profile races," he said. "So the fact that this is so close for so long, this is different.”
The battle to fill the seat left open by outgoing Republican Sen. Jeff Flake has led to a close race between two sitting congresswomen.
Republican Rep. Martha McSally started out with a slight lead, but as more and more votes have been counted, Democratic Rep. Kyrsten Sinema has taken over and is widening her edge.
The race has turned into more of a marathon than a sprint, with daily updates on how many votes still need to be counted in Arizona's more populous county, Maricopa.
The Maricopa County Recorder’s Office, which is tasked with counting the results in Phoenix and surrounding areas, has given daily updates since Thursday. The office had about 345,000 votes to process that day, and has processed between 36,000 and 79,000 votes every day since.
The office's latest update on Sunday reported that it had about 162,000 still left to process.
Other counties in the state still have votes left to process, too. As of Sunday evening, the total number of votes needed to be counted in Maricopa and five other counties was approximately 219,800, according to the regularly updated Twitter account of an analyst in the Arizona Secretary of State’s office.
The delay in processing the votes stems from Arizona’s practice of allowing voters to mail in ballots up until and through Election Day. Those ballots then have to be verified based on the signature on the outside of the ballot.
If it isn’t instantly matched against the signature that voter has on record, voting officials have to reach out to the voter to verify it.
Another factor adding pressure to the count is a recent court decision, which The Arizona Republic reports was prompted by a lawsuit from the state's Republican Party. It stipulates that all counties have to use the same signature verification process but only have until Wednesday to do so.
Maricopa County Recorder Adrian Fontes released a statement Monday afternoon reiterating that the Wednesday deadline isn’t “for counting ballots” but serves as a deadline for voters to verify their eligibility if they cast a provisional ballot and to verify the signatures of mailed-in ballots that were dropped off on Election Day.
“We will likely continue the tabulation of ballots into the weekend,” Fontes said in the statement.
Herrera said there may be efforts to extend the deadline, but the status of the vote tally by Wednesday could also play a role and make an extension unnecessary.
“If by Wednesday every single vote hasn’t been verified, there will still be enough for a result to be known just given the margin between the two candidates,” he said.
“If it doesn’t narrow, then, given the outstanding votes, it would be so unlikely that the vote would change that they would probably call the election anyway," he said. "And if it did narrow, there may be some efforts to extend the deadline.”
Both candidates have put out statements over the past week touting what they perceived as different victories from various vote counts in different counties.
The most recent statements from the campaigns came on Sunday, when McSally campaign CEO Jim Bognet released a statement saying, “The latest release provides compelling evidence that the remaining uncounted ballots are favorable to Martha. And we will continue our effort to make sure all lawful ballots are counted.”
Meanwhile, Sinema campaign manager Andrew Piatt also released a statement on Sunday arguing that her lead was “insurmountable.”
“Kyrsten has now expanded her overall lead to 32,640, or 1.52 percent, meaning McSally would have to win the remainder of Maricopa County ballots by 22 percent to take the lead in this race,” Piatt said in a statement based on the numbers as of Sunday evening. “This is not plausible. Kyrsten will be declared the next U.S. Senator from Arizona.”
Either way, the race will be historic. Either candidate would become the state’s first female senator.
And if Sinema wins, she would become the first Democratic senator to represent the state since 1995.
Herrera called this a “very unusual” race, noting how “turnout was high, higher than usual."
"And again, going into it the Republican candidate would have an advantage ... ” he said. "This result is very out of the ordinary."