Democrats made significant gains Tuesday in late ballot counts for two key undecided House seats in Southern California as post-election tallies continue to swing in their favor and against Republicans.

Democrat Katie Porter pulled ahead of incumbent GOP Rep. Mimi Walters in Orange County’s inland 45th District, while the battle for the 39th showed Democrat Gil Cisneros pulling close to even with Republican Young Kim.

If those patterns continue, it’s possible Orange County – which Ronald Reagan famously described as “the place good Republicans go to die” – soon will have no GOP representatives in Washington D.C., after Republicans lost two other local House seats this cycle.

Porter has a 261-vote lead over Walters, overcoming the 6,200-vote advantage that the congresswoman held on election night. Porter has won more than 56 percent of the ballots counted since election night.

In the race for the 39th Congressional District – which crosses Orange, Los Angeles, and San Bernardino counties – Cisneros pulled within 711 votes of Kim, erasing much of the nearly 3,900-vote lead she had a week prior. Cisneros has won nearly 55 percent of the votes tallied since the election.

Post-election tallies of provisional and late vote-by-mail ballots have tilted in favor of Democrats in many parts of California, helping the party’s candidates catch or overtake Republicans who were ahead on Election Day. Late ballots historically have tended to favor Democratic candidates, because left-leaning populations frequently cast their mail ballots closer to the election.

There remained 261,600 uncounted ballots in Orange County, 688,000 in Los Angeles County, and 192,400 in San Bernardino County. It could take weeks to have final, official results in those contests.

On Wednesday, Porter plans to attend an orientation in Washington D.C. for new House members, signaling her confidence in the contest’s outcome, said an aide with her campaign.

Walters’ campaign didn’t immediately return calls for comment.

In the contest for the 39th, both campaigns worry that the margins could come down to a handful of votes and volunteers working for each candidate have swarmed local registrar of voters’ offices during the past week. There, they’ve quarreled over the tallying process and attempted to get a small number of ballots rejected for having signatures that don’t match voter rolls.

That fight has turned nasty. Both campaigns accused the other over the weekend of attempting to improperly interfere with the process. On Monday, Kim’s campaign issued a statement alleging without evidence that Cisneros’ volunteers in Los Angeles had physically tampered with ballots. Her campaign also contended that if the remaining ballots swing in Democrats’ favor, it could be due to “foul play.” In response, top voting officials in Orange and Los Angeles counties said that no such tampering had occurred, assuring the public of the counts’ validity.

Cisneros’ campaign manager, Nic Jordan, issued a statement Tuesday saying that voters who mailed in their ballots close to election day or dropped them at precincts, and those who voted provisionally — all of which are categories of ballots being counted in late tallies — favored his candidate.

“Every time there has been a significant number of ballots counted since Election Day, Gil Cisneros has gained ground, and today’s results from both Los Angeles County and Orange County further demonstrate that fact.”

Kim’s campaign didn’t comment on its narrowing lead, but said it would work to ensure “that every legal ballot cast is counted.”

Democrats spent heavily this election to flip seven Republican-held House seats in California. So far, Democrats have managed to take four of those districts, including winning Rep. Darrell Issa’s open seat and defeating 30-year Rep. Dana Rohrabacher. Late Tuesday, the Associated Press declared that Democrat Josh Harder had defeated incumbent Republican Rep. Jeff Denham in the 10th Congressional District. Three other races remain too close to call.

Orange County will update its vote counts daily, except Sunday, until all the ballots are counted. Los Angeles County updates its count on Tuesdays and Fridays. San Bernardino County will update its tally on Wednesday and intermittently afterward.