INDIANAPOLIS (AP) — The counting of mail-in ballots continued Wednesday night in the hotly contested race for a central Indiana congressional seat that remained too early to call.

Republican Victoria Spartz and Democrat Christina Hale faced each other for the seat that’s been a GOP bastion for decades.

The campaign was largely fought in the northern Indianapolis suburbs amid softening support among suburban women for Republicans under President Donald Trump. The winner will replace Republican Rep. Susan Brooks, who didn’t seek reelection this year.

An uncertain number of mail-in ballots, many of which were in Marion and Hamilton counties, remained uncounted Wednesday night.

Hamilton County workers faced counting about 28,500 mail-in ballots that were received by Tuesday’s noon deadline but weren’t tallied that day, said Beth Sheller, elections administrator in the county just north of Indianapolis.

The district covers roughly the northern third of Indianapolis, which also received a record number of mail-in ballots. Election workers in Indianapolis started Wednesday needing to process some 90,000 mail ballots and would likely need until Thursday to complete counting them, said Russell Hollis, deputy director of the Marion County clerk’s office.

Spartz was cheered by supporters as they celebrated the preliminary vote count late Tuesday.

“We know they’re still counting the vote, but we feel that we’re on a good track to win,” Spartz said.

Hale did not speak in public Tuesday night, with her campaign saying it was still monitoring the vote totals.

“There are still tens of thousands of mail-in votes in the Fifth District that have not yet been counted, particularly in Marion and Hamilton counties, where we have done a significant amount of voter outreach over these past few months,” Hale campaign manager Joann Saridakis said in a statement. “This race is not over.”

At least $15 million was sunk into the race, with national party organizations and dark-money groups spending heavily on largely negative advertising.

The congressional race became a partisan battleground as cracks in the Republican dominance have appeared in the past couple years in the 5th District, which stretches from the north side of Indianapolis north into rural areas and the smaller cities of Anderson and Marion.

Democratic U.S. Sen. Joe Donnelly won in the district even as he lost statewide in 2018 to Republican Mike Braun and a handful of Democrats won city positions in the northern Indianapolis suburbs for the first time during 2019 municipal elections.

Spartz, 42, a state senator from Noblesville who immigrated from Ukraine, won the Republican primary after flooding TV screens and mailboxes with ads fueled largely by some $1.2 million she loaned to her campaign. That enabled her to build name identification after two years in the state Senate.

Spartz campaigned as more stridently conservative than Brooks, who built a reputation as a moderate Republican in comfortably winning four elections.

Hale, 49, is a former state representative from Indianapolis who was the 2016 Democratic nominee for lieutenant governor. Hale leaned heavily during the campaign on her personal story of working as a waitress and struggling with daycare for her son as a single mom while earning a college degree.