PHOENIX (NewsNation) — Margins between Democrats and Republicans have narrowed considerably Thursday in Arizona’s race for U.S. Senate and governor, but the races remain too close to call two days after the election.

This comes as election officials have been chipping away at more than half a million mail ballots returned on Election Day and shortly before — some 600,000 ballots left to count, a quarter of the total cast.

Protracted vote counts have for years been a staple of elections in Arizona, where the overwhelming majority of votes are cast by mail and many people wait until the last minute to return them. But as Arizona has morphed from a GOP stronghold to a competitive battleground, the delays have increasingly become a source of national anxiety for partisans on both sides.

After opening big leads early on election night, when only mail ballots returned early were reported, Democrats have seen their leads dwindle as more Republican ballots have been counted. On Thursday morning, Democrats led in the races of Senate, governor and secretary of state, while the race for attorney general was essentially tied. It could take several days before it’s clear who won some of the closer contests.

Incumbent Democratic Sen. Mark Kelly and Republican challenger Blake Masters are mired in a tight race that has yet to be called because of an influx of mail-in ballots still being tabulated in Maricopa County. State officials have said it will likely take until at least Friday to have almost all of the ballots counted.

Kelly’s camp told NewsNation, “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.”

Kelly, a former astronaut, held a 51% to 46% lead over Masters as of Thursday morning. An estimated 78% of votes have been counted according to Decision Desk HQ.

In Arizona’s race for governor, Kari Lake, a former television news anchor and candidate endorsed by former President Donald Trump, is up against Democrat Katie Hobbs.

Despite the tight race, Lake said she feels “100% certain” she’s going to win.

The gubernatorial race has been centered heavily on Lake’s baseless claims of fraud in the 2020 election. The Republican candidate for attorney general also trailed narrowly.

Hobbs held a 50% to 49% lead over Lake as of Thursday morning. An estimated 77% of votes have been counted, according to Decision Desk HQ.

Hobbs released a statement Tuesday, saying she has “every confidence that the counties administering this election conducted a free and fair election, and their results will be accurate. But they will take time, so prepare for a few more days of counting.”

See full results for Arizona as they come in.

The Associated Press contributed to this report.