WASHINGTON — A closely divided U.S. House could face an unusually high-stakes battle over disputed congressional races after the November midterm elections, with lawmakers holding constitutional and statutory powers to investigate contests and decide whom to seat. The House and Senate are the final judges of their own elections, said John C. Fortier, a senior fellow at the American Enterprise Institute. That means Congress can question a state-certified result, although the practice is now rare compared with the 19th century. The possibility has drawn renewed attention as Republicans worry about losing control of the House. A handful of unresolved races could determine which party holds the majority, creating incentives for candidates and lawmakers to challenge results or delay the seating of members-elect. The process begins at the state level. After votes and any recounts are completed, a state’s top election official generally certifies the winner and sends a certificate of election to the House clerk. But certification can be delayed during a legal dispute or amid concerns about the integrity of the vote. That happened after the 2020 election in New York, where officials held up Republican Claudia Tenney’s seating while her extremely close race was litigated. She did not take the oath until February 2021, more than three months after Election Day. North Carolina’s 9th Congressional District offered an even more dramatic example after the 2018 election. The state board declined to certify either Republican Mark Harris or Democrat Dan McCready after evidence emerged involving absentee ballots. Following testimony that a political operative had organized a fraudulent ballot operation, the board ordered a new election. Republican Dan Bishop won the special election that followed. The House could also act on the first day of a new Congress, when members-elect gather to elect a speaker before being sworn in. Any member-elect may object to another member-elect taking the oath. A similar effort occurred in January 2021, when Texas Republican Chip Roy objected to lawmakers from six states taking their oaths. The Democratic-controlled House rejected the move by a vote of 371-2 and directed the speaker to swear in the members. Under House procedures, lawmakers can provisionally seat a disputed member and refer the matter to the House Administration Committee. They can also refuse to seat either claimant while the committee investigates. The Congressional Research Service has said refusing even provisional seating would be appropriate only in exceptional circumstances and has occurred just a few times since 1933. A separate route is available under the Federal Contested Elections Act of 1969. A losing candidate may file a challenge, but must show that alleged irregularities or fraud changed the outcome and that the challenger would have won without them. The House Administration Committee can subpoena and preserve election materials, including ballots, voting machines, poll books and absentee-ballot records. It may rely on the state’s count or conduct its own recount. After investigating, the committee makes a recommendation, and the full House decides by a simple majority whether to seat one candidate or leave the seat vacant. Those decisions would be made by the new House that convenes in January, not by the outgoing Congress during the post-election lame-duck session. Investigations can take months. In the closely contested 2020 Iowa 2nd Congressional District race, Democrat Rita Hart challenged Republican Mariannette Miller-Meeks’ victory. The case ended when Hart withdrew her challenge in April 2021. Casey Burgat, a legislative affairs professor at George Washington University, said the risk of partisan brinkmanship would rise sharply if the majority were narrow. Parties could have greater reason to search for grounds to delay or deny the seating of opposing lawmakers, he said. The seriousness of a challenge could depend on who leads it, Burgat said. A move by a prominent party leader would likely carry more weight than one brought by a lawmaker known primarily for provocation. The outcome, he suggested, could depend on how far congressional leaders are willing to push institutional norms to secure power. Some Democrats have also expressed concern that the House clerk could manipulate the list of members-elect used in the speaker’s election. Election-law experts described that scenario as highly unlikely. The clerk’s role is generally ministerial: once a state election official certifies a winner and transmits the credentials, the clerk places that person on the roll. The stakes are especially high because the House must elect a speaker before it can conduct other business. Still, experts said the clerk is not authorized to disregard valid state certificates or independently decide which members may vote. The broader lesson from the 2020 election and the Jan. 6, 2021, attack on the Capitol is that election safeguards depend not only on written rules but also on officials’ willingness to follow them. In a narrowly divided House, legal mechanisms designed for exceptional disputes could become tools in a partisan struggle over who represents voters and which party controls Congress.