Rep. Kyrsten Sinema (D) has increased her lead over rival Rep. Martha McSally Martha Elizabeth McSallyThe Hill's Campaign Report: Presidential polls tighten weeks out from Election Day Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' New ABC/WaPost poll finds Trump edging Biden in Arizona, Florida MORE (R) in the race for an open U.S. Senate seat in Arizona on Monday as several counties made progress getting through thousands of yet-uncounted votes.

Sinema now leads by a margin of 38,197 votes, or about 1.7 percentage points, out of more than 2.1 million votes cast.

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Worryingly for McSally, the largest county with a batch of uncounted votes likely to benefit the Republican neared the end of its count Monday without cutting significantly into Sinema’s lead.

Officials in Pinal County, where McSally leads by about 12 points, said Monday that they had completed counting early ballots. The county still has about 6,000 votes left to count, though they are provisional ballots that may tilt toward Democrats.

The largest remaining batch of ballots will come from Maricopa County, the state’s most populous county. Sinema leads in Maricopa County by about 3.5 percentage points, a margin that has grown as the final early and absentee ballots have been counted.

Maricopa County reported an additional 19,000 ballots on Tuesday.

The only other large number of ballots to be counted come from liberal Pima County, which Sinema won by almost 15 points.

The dwindling number of ballots to be counted is a troubling sign for McSally, who led the vote on election night before hundreds of thousands of early votes cast in the final days before Tuesday’s midterm elections were counted.

Republicans feared McSally might not regain the lead she lost when new vote tallies were reported Thursday, though they held out hope that the ballots to be counted early this week would come from voters who dropped off their absentee ballots on Election Day.

Voters who cast ballots on Election Day in Arizona tend to be more Republican, but Sinema’s lead means they would have to be substantially more Republican than average to give McSally a decisive edge.