IOWA CITY, Iowa (AP) — Iowa officials on Monday certified a Republican candidate as the winner by six votes of an open seat in the U.S. House, in what is shaping up to be the closest congressional election in decades.

Republican Mariannette Miller-Meeks finished ahead of Democrat Rita Hart in Iowa’s 2nd Congressional District after a recount saw her 47-vote lead steadily dwindle to single digits.

The state Board of Canvass voted 5-0 Monday afternoon to certify Miller-Meeks as the winner over Hart by a count of 196,964 to 196,958.

The board, which includes Gov. Kim Reynolds and four other state elected officials, also certified President Donald Trump as the winner of the state’s six electoral votes. The board is made up of three Republicans and two Democrats.

If it withstands expected legal challenges, Miller-Meeks' margin of victory would amount to the closest U.S. House race since 1984 and the tightest in Iowa since 1916.

“That race alone reinforces that every vote counts and can make a difference,” said Secretary of State Paul Pate, Iowa's commissioner of elections and a canvass board member.

Hart’s campaign has signaled that it will likely take legal action to challenge the outcome, and must do so within two days of the certification under Iowa law. Such a filing would trigger the formation of a contest court consisting of Iowa Chief Justice Susan Christensen and four district judges who will be appointed.

The tribunal would have the discretion to set rules that are “necessary for the protection of the rights of each party and speedy trial of the case.” Hart could be required to post a bond that would cover the costs if the contest isn't successful.

The panel would be expected to move quickly and rule on which candidate is entitled to hold the office by Dec. 8.

If the court ruled in favor of Miller-Meeks, Hart could file a final appeal with the Democratic-controlled U.S. House, which has the power to judge its members’ elections and has intervened in the past on rare occasions.

Miller-Meeks declared victory after Saturday's recount in Clinton County, the last in the district, cut her lead from eight votes to six.

“While the race is extraordinarily close, I am proud to have won this contest and look forward to being certified as the winner,” she said. “It is the honor of a lifetime to be elected to serve the people of eastern and southern Iowa. Iowans are tenacious, optimistic and hardworking, and I will take those same attributes to Washington, D.C., on their behalf.”

Miller-Meeks, a state senator from Ottumwa, is making her fourth run for Congress. She lost her three previous runs for the seat in 2008, 2010 and 2014 to Democrat Dave Loebsack, whose retirement after seven terms created the vacancy.

Hart's campaign manager Zach Meunier said after Monday's certification that the recount was designed to count ballots that had already been tallied and that “additional legal ballots may have yet to be counted.”

“Over the next few days, we will outline our next steps in this process to ensure that all Iowans' voices are heard,” he said.

If Miller-Meeks prevails, her victory would limit the size of the Democratic majority in the House, which stands at 222-206 with seven races still undecided, according to race calls by The Associated Press.

If Hart appeals the results to the five-judge panel, the AP will not call the race until after the panel issues a ruling.

The state’s certification came after the 24 counties in the district approved the results of their recounts, which collectively added 143 votes for Hart and 102 votes for Miller-Meeks.

The most dramatic swing came in the district's most populous, Scott County, where Hart netted 26 votes. Scott County Supervisors on Monday certified that change, while saying they were troubled that the recount board tallied 131 more absentee ballots than an earlier post-election canvass.

County officials said they were baffled by the source of the discrepancy, which could be from the discovery of uncounted ballots, a machine counting error or a mistaken double count. County Attorney Mike Walton said the board had no choice but to certify the recount board’s work.

“It’s not perfect,” he said. “There are questions that one side or another may want answered through a contest.”