The 2020 election was one of the most contested presidential races in recent history, with former President Donald Trump seeking to reverse losses in key states such as Georgia through various challenges to the certification of the results, which showed President Joe Biden as the victor.

Four years later, the race for the White House is expected to be close again, and in several states, election procedure has left the door open for election challenges, which could prolong the battle for the presidency. Here are three states where action, or inaction, could leave the door open to lengthy challenges to the Nov. 5 election.

Georgia

The State Election Board, which no longer includes the Georgia secretary of state, has passed multiple measures in recent months that have changed election procedure in the critical swing state.

The main procedure change, which could extend the fight for the Peach State, states that local election officials may conduct a “reasonable inquiry that the tabulation and canvassing of the election are complete and accurate and that the results are a true and accurate accounting of all votes cast in that election” before certifying the results.

The measure was passed in August and has prompted a Democratic legal challenge over the problems it could cause with the timeline for certifying the state’s election results.

Another rule change that has caused concern over the speediness of getting Georgia’s election results is the board’s rule requiring all counties to hand-count all ballots, in addition to machine tallies, for the November election.

Pennsylvania

In the Keystone State, deadlines for certifying the election prior to the meeting of the Electoral College could be a problem because the state has yet to pass a law mandating certification before necessary deadlines.

Congress passed reforms to the certification process for presidential elections in 2022, after a chaotic certification process for the 2020 election, with the Electoral Count Reform and Presidential Transition Improvement Act of 2022.

The law dictates that a state must issue its certificate of ascertainment by Dec. 11, 2024, but unlike several other key battleground states, Pennsylvania has yet to establish firm deadlines for recounts and litigation to be completed by that time. Legislation to establish firm deadlines has passed through the state House but has yet to be acted on by the state Senate.

While the federal law allows for courts to issue a certificate of ascertainment by Dec. 16, the day prior to when the Electoral College will meet, the inconsistency between state and federal law deadlines could cause doubt by lawmakers and activists — and possible challenges at the certification of the results during a joint session of Congress on Jan. 6, 2025.

Wisconsin

In the Badger State, a similar issue to Pennsylvania could occur as the state has yet to establish firm deadlines for certification ahead of new federal deadlines — which could be exploited to delay or cast doubt on certification of the results.

Democrats in both Pennsylvania and Wisconsin have sounded the alarm over the problems that could arise from the gap between state and federal law, suggesting that though unlikely, it could present problems.

“The danger is that if we don’t meet the deadline, we open ourselves up to further litigation,” Democratic state Rep. Lee Snodgrass told Reuters. “There could be litigation on everything.”

While challenges to the results of different states can still be brought up at the Jan. 6 meeting of Congress, the 2022 electoral count law has raised the bar for objections during the session. Under the new law, a fifth of members of both the House of Representatives and the Senate must sign off for an objection to be filed.

Georgia, Pennsylvania, and Wisconsin are expected to be some of the closest states in the battle for the White House between Trump and Vice President Kamala Harris. In 2016, Trump won all three states en route to an Electoral College victory, while in 2020, Biden won all three states en route to an Electoral College victory.