Rep. Cathy McMorris Rodgers has gained ground in every corner of Spokane County as ballots have trickled in since election night and extended a district-wide lead that remains within striking distance for challenger Lisa Brown.

A lead that was 600 votes Aug. 7 has swelled to 6,976 votes as of Tuesday’s ballot returns for McMorris Rodgers, who is facing the toughest fight to retain her seat in her 14 years in Congress. However, late ballot returns have continued to show improvement for the incumbent throughout Spokane County, an important battleground in a district that local and national Democrats hope to turn blue in November.

McMorris Rodgers has whittled an 8 percentage point deficit to Brown in Spokane County on election night down to less than 2 percent, picking up a larger share of late votes in every corner of the district’s most populous county than what she posted last Tuesday. That includes the core of Spokane’s downtown, one of the few Democratic strongholds east of the Cascades.

In portions of the 3rd Legislative district within Spokane County, which is currently served exclusively by Democratic lawmakers in Olympia and likely to remain that way after the general election, McMorris Rodgers continued to lag behind Brown in late returns.

However, the margin was less significant than it appeared on election night. Of those ballots counted in the last seven days in the 3rd district, McMorris Rodgers captured 36 percent, which was ahead of the 31 percent she received on election night. Brown received 60 percent of the late returns in the same area, down from her election night total of 62 percent but still widely outperforming the incumbent.

The same was true in the 4th, 6th, 7th and 9th district areas of Spokane County, as McMorris Rodgers captured larger shares of the late vote in all those regions. Both candidates are virtually tied in late voting in the 6th district regions of Spokane County, which showed strong returns for Democrats on election night but whose races have become more competitive for the GOP in recent days, with Rep. Jeff Holy pulling ahead of Jessa Lewis for the state Senate seat and Rep. Mike Volz within about 60 votes of Democratic candidate Kay Murano to retain his seat in the House of Representatives.

Brown’s performance did not keep pace with McMorris Rodgers’ vote pickup in late voting, dropping her below 50 percent of the total vote in Spokane County. But the Democrat is still on track to lead the county’s primary vote based on strong early voting totals. That would make her the first Democrat to carry Spokane County against McMorris Rodgers since 2004, the first time the congresswoman ran for Congress.

Brown has done that by posting large margins in a cluster of precincts in Spokane County, mostly in Spokane’s South Hill. But Brown’s share of precinct leads has also fallen in the past week. On election night, Brown was ahead of McMorris Rodgers in 198 precincts, while the Republican led in 158 precincts. By Monday, the numbers had shifted, with McMorris Rodgers leading in 191 precincts, compared to Brown’s 164 precincts. The different totals are due to ties.

Mike McLaughlin, the county’s elections manager, said it’s typical to see Republican vote totals climb in the days following an election.

“It’s generally true, Democrats vote early, and Republicans vote later,” he said.

That’s played out in all of McMorris Rodgers’ re-election bids. Her share of the vote total from election night to final certification has risen in every contest since at least 2012. This year’s jump of 1.65 percentage points is close to what she saw in that 2012 campaign, when her vote share against Democrat Rich Cowan edged up 1.8 percentage points in the weeks after the primary. The difference is McMorris Rodgers had already collected a majority of the vote in 2012, with Cowan around 35 percent, while the congresswoman has failed to reach a majority in this year’s primary returns.

Vicky Dalton, the Spokane County auditor, said the late returns for McMorris Rodgers this year were not significantly different than those previous election returns. She pointed to 2006, when late Republican votes shifted countywide results up to six points in local races.

“This is an unusual year in the passion of voters,” Dalton said, noting that election workers had seen an uptick in split-ticket ballots that couldn’t easily be explained.

Also different in this year’s election is the tenor of the campaign. McMorris Rodgers began airing negative ads painting Brown as a western Washington liberal early in the contest, before primary ballots had even hit mailboxes. Brown has responded with ads of her own criticizing McMorris Rodgers chiefly for her votes on health care.

It’s difficult to say what effect those ads had on Brown’s share of the late vote total, said Travis Ridout, professor of political science at Washington State University in Pullman.

“It is complicated, and it’s hard to untangle,” Ridout said. “I think there is some research that suggests that when people are exposed to negativity about a candidate, that they’re less enthusiastic about voting for that candidate.”

The McMorris Rodgers ads, attacking Brown’s record on taxes and public safety, probably didn’t sway those who had their minds made up to cast ballots for the Democrat, Ridout said. But for those who were still undecided and leaning toward Brown, the ads may have dissuaded them not to vote at all, he said, which could account for the difference in late numbers between her and McMorris Rodgers.

“People who are exposed to a lot of negative information about a candidate they already support, they’re more likely to just not vote,” he said.

Final results of the primary vote must be certified by Tuesday. There were 2,200 ballots left to count in Spokane County after the last tally.