Democrat Mark Herring, left, and Republican Mark Obenshain participate in a campaign debate on Oct. 2 in Leesburg. (Jahi Chikwendiu/The Washington Post)

After the first day of the recount in Virginia’s election for attorney general, Democrat Mark R. Herring appeared to have widened his narrow lead over Republican Mark D. Obenshain with a net gain of 91 votes in Fairfax County, officials said.

The preliminary results injected another round of uncertainty into a race that Obenshain led on election night but that swung to Herring during the subsequent topsy-turvy days when election officials canvassed the tallies and discovered numerous errors.

Volunteers labored away in three jurisdictions where recounting began Monday in the closest statewide election in Virginia history. While most of the state will start counting Tuesday, Fairfax started Monday because of its large size — and Alexandria and Chesapeake did so because their voting equipment requires them to recount ballots by hand.

More than 2.2 million people cast votes in the down-to-the-wire election, which led to canvasses and some controversy before the State Board of Elections declared Herring the winner by just 165 votes. That tiny margin entitled Obenshain to a government-funded recount.

The recount puts more at stake than who will serve as Virginia’s next top lawyer; it will also determine whether Democrats succeed in sweeping all three statewide offices up for election last month for the first time in a generation.

Cameron Quinn, general registrar for Fairfax County, opens provisional ballots from Fairfax County voters for the attorney general race on Nov. 12. (Bonnie Jo Mount/The Washington Post)

Additionally, the outcome will set in motion a domino effect that could affect control of the General Assembly by forcing a special election to the state Senate, where both candidates serve. If Obenshain wins, his conservative district in Harrisonburg is likely to elect another Republican to replace him. But if Herring wins, his seat in suburban Loudoun County could be highly competitive — and a GOP win would shift Senate control to the Republicans. The House of Delegates is overwhelmingly controlled by the GOP.

In Fairfax County on Monday, with a third of the county’s 240 precincts counted, Herring had gained an additional 183 votes, while Obenshain saw 92 more votes fall into his column, said Brian W. Schoeneman, secretary of the county’s board of elections.

According to a Herring campaign attorney, the gain was even bigger when all three jurisdictions were added together, resulting in a new winning margin for the Democrat of 305 votes.

The change in totals, plus other gains for Herring in Alexandria and Chesapeake, further bolstered the confidence of the Democrat’s campaign, while Obenshain’s camp cautioned that the recount process, scheduled to end at 11:59 p.m. Wednesday, was far from over.

“Having seen the early recount results, we are more confident than we were even at the beginning of this recount” that Herring will prevail, the Democrat’s attorney, Marc Elias, said, during a conference call with reporters to announce preliminary results.

Obenshain spokesman Paul Logan said it was “too soon to draw conclusions” about what the ultimate result would be.

“What we have seen so far today, as we expected, is that the numbers have already started to change, as the second, more thorough count is conducted,” Logan said. “That’s why it was important to go through the recount and to give Virginia voters the assurance they deserve in this historically close election.”

Other jurisdictions will start their recounts Tuesday. On Friday, a three-judge panel in Richmond is expected to rule. Several thousand votes are potentially in play because machines didn’t read ballots filled out incorrectly, leading to high tensions all around, officials said.

“This thing is historic; we’ve never done anything like this before,” Seth Stark, chairman of the Fairfax County elections board, said while 40 teams of two volunteers and an observer from each campaign settled in to recount about 306,000 votes.

Even so, the process was mundane, with the bulky black optical scan machines almost noiselessly sucking in each new ballot inserted before rattling out new vote counts for each precinct on ticker tapes. Sometimes, the ballots got stuck, prompting the volunteers to shake a machine back and forth or bang on its side like an old TV set. Officials paid special attention to ballots not read by the machines because voters did not completely fill in the circles next to their candidate’s name, circled the name instead, voted for more than one candidate or made some other mistake.

“It’s a technical process,” one worker inside the Fairfax courthouse joked, over a steady hum of chatter.

In such instances, the ballots were separated and, for the first time, examined and hand counted, Schoeneman said.

Most of the changes in Monday’s tally came from such ballots, and the county estimates that about 5,500 in total would have to be pulled aside, he said.

At least one ballot had “Mickey Mouse” as a write-in candidate, while others bore check marks, half-filled circles or other problems that kept the optical scan machines from properly reading them, Schoeneman said.

In cases in which the machine could not read a ballot, the teams were required to examine the vote for “clear affirmative intent,” where it seemed obvious which candidate was chosen, officials said.

Ballots on which a voter wrote in a candidate’s name instead of filling in the designated circle were tossed out, officials said, citing state election codes.

Any ballots in dispute were set aside and delivered by state police to the panel of judges in Richmond, which will convene Wednesday to begin reviewing those challenges and hearing disputes between the two parties.

As the day reached a close Monday, no ballots were challenged in Fairfax or Alexandria, officials said. In Chesapeake, where 15 teams pored through ballots in 65 precincts, officials did not release any details.

Fairfax, in particular, has been the site of controversy in the race because of its handling of provisional ballots cast in cases in which voters lacked identification, went to the wrong polling place or never received an absentee ballot after requesting one.

The county gave more time than other jurisdictions to allow provisional voters to appear in person to explain their ballots. Republicans objected to that extra time, although the board said it was acting legally. Such complaints could come into play if the loser chooses to take the race to the legislature, as allowed by Virginia law. Obenshain’s attorney, William H. Hurd, said in court last week that the Republican “may wish to consider that possibility,” though he later called such talk “premature” and “hypothetical.”

Obenshain’s campaign also said this month that it was “distressed by the lapse in ballot security” in Fairfax because some ballots were not delivered to the county clerk for safekeeping as quickly as they should have been – an assertion that Fairfax officials said has no evidence.

Schoeneman said mistakes on election night are bound to be discovered because “this is a human process” and “there is no such thing as an error-free election.”

For example, he said, in the county’s Cameron Glen precinct, officials learned that the sign-in sheet on election night had 13 more voters than votes counted. Herring gained eight of those votes and Obenshain gained five, according to a running tally posted on a dry erase board just outside the Jury Assembly Room, where most the recounting was being done.

“I would expect there’s going to be one or two more [such cases] here and there,” Schoeneman said.

“Unfortunately, given the size of Fairfax County and the closeness of this race, that may have an impact,” he said. “But it’s too early to tell, at this point, what that impact may be.”

Ben Pershing contributed to this report.