What happens if we don’t know who our president is on Election Day?

Editor’s Note: Ross Garber is a political investigations, elections and impeachment lawyer and teaches at Tulane Law School. The opinions expressed in this commentary are his own. View more opinion at CNN

We should be prepared for the likelihood that we won’t know who our next president is on Election Day.

Ballots will continue to pour in for days afterwards, close results in key states will likely trigger recounts, and there will almost certainly be disputes and litigation.

President Trump and his supporters may well allege that mail-in ballots are tainted by fraud. There will no doubt be disagreements about whether some ballots were improperly disqualified and about whether ballots that arrive after Election Day are valid.

There may be allegations and investigations of foreign interference. President Trump has warned that problems with mail-in voting might result in our not knowing the results for months or years. Both candidates will have massive teams of lawyers deployed to monitor activities and raise concerns at polling places all across the country.

Particularly in swing states, challenges and litigation over a host of potential legal issues could drag on. That is not likely to be the end – even when the votes are tallied.

But the election calendar doesn’t permit unending bickering. In fact, it is a strict referee with a sharp whistle.

Keep an eye on December 8. This is the date set by a federal statute (3 U.S.C. 5) as the deadline for final resolution of all election disputes, including court challenges. If there isn’t finality by then, Congress doesn’t have to presume that the electoral votes submitted by that state are valid. It’s referred to as the “safe harbor” deadline.

It’s the reason why the Supreme Court in Bush v. Gore stopped the Florida recount, effectively handing the election to Bush.

The Court said that Florida wanted to get the benefit of the safe harbor provision but there was no way all disputes and recounts could be completed that day, so the recounts should cease. Bush was ahead, so he got Florida’s electoral votes and consequently became President.

December 8 is roughly one month from Election Day. It’s difficult to imagine that this safe harbor date will be met by swing states – particularly given the dramatically increased use of mail-in ballots and disagreements about their tabulation. In fact, one candidate or the other may have an incentive to maintain uncertainty until after that date for reasons I’ll get to in a moment.

Maybe the Supreme Court will step in, as it did in Bush v. Gore, and award the presidency to Trump or Biden before December 8. But we shouldn’t count on it. And, if not, there’s a process for what comes next.

Just six days after the safe harbor date, on December 14, the members of the Electoral College meet in their respective states. But there could be disputes about who those electors are. Imagine if in Michigan, for example, Trump is ahead in ballots received by Election Day, but that counting ballots that arrive after Election Day would give Biden the win. The Michigan Secretary of State, a Democrat, might certify a Biden win, naming a Biden slate of electors. The Republican legislature might purport to overrule that certification and name a Trump slate of electors, even though, under state law, it has no authority to do this.

This scenario with competing slates of electors has happened before, on a large scale in 1876, in the race for president between Rutherford B. Hayes and Samuel Tilden, where Republicans and Democrats in key states submitted competing slates of electors. In 1960, Hawaii submitted two sets of electors, and members of the Florida legislature contemplated submitting a competing slate of electors in the 2000 election. Even if competing slates of electors aren’t submitted, there may still be disputes about whether the single slate of electors submitted by a state is valid, likely because of allegations of fraud or other irregularities.

So, how are issues related to disputed slates of electors resolved? Here’s how it works.

On January 6, the House and Senate meet together to count Electoral College votes. A statute (3 U.S.C. 15) says that the House and Senate vote separately on objections to recognizing the validity of electors. If the House and Senate disagree, a law says Congress is to defer to the governor of the state to determine which votes are valid. But, some scholars, and the Congressional Research Service, have noted issues in interpreting and applying this provision, particularly in a situation in which only one slate of electors has been submitted in a timely fashion pursuant to state law.

What if, because there is a tie or because Congress decides to not recognize any slate of electors from some states, neither candidate gets a majority of electoral votes? Then, under the 12th Amendment, the House decides the president and the Senate decides the vice president. The House vote is taken by state, so each state has one vote. Right now, even though Democrats have a majority in the House, Republicans control a majority of state delegations. If the composition of the House stays the same, and if members all vote along party lines, the House would almost assuredly elect Trump as president. If the Senate composition stays the same, a party line vote would mean Mike Pence as vice president; if Democrats take control, it would be Kamala Harris.

I’m certainly not purporting to identify all the potential disputes, just some of the biggest ones, but there’s yet another potential curveball I want to introduce. This voting by the House and Senate would happen after new members are sworn in. But remember how we got here in the first place: vote counting disputes. There could very well be disputes about who won Senate and House races. The Constitution says each house of Congress gets to decide disputes about their respective memberships. Indeed, there could be a massive fight about who will be seated in Congress before we even get to the fight about who will be president and vice president.

But these fights don’t go on forever.

If the dust hasn’t settled in the race for president by January 20, the date set by the Constitution for Inauguration, then the 20th Amendment says the vice president elect serves as acting president until a president is chosen. If no vice president has been designated by then, the 20th Amendment provides that Congress determines how an acting president is selected.

The Presidential Succession Act provides that the Speaker of the House is next in line, followed by the President Pro Tempore of the Senate. Here, imagine if Democrats retain control of Congress but know that a vote by state delegation would mean a Trump presidency. The Democratic Speaker and her caucus might play hardball and intentionally delay relevant votes to force the Speaker’s succession to the presidency.

This is not some political fever dream. Congress has decided presidential elections in the past. In 1800, the House selected Thomas Jefferson as President, and in 1824, it chose John Quincy Adams. In the disputed 1876 election, with the aid of an Electoral Commission, Congress selected Rutherford B. Hayes as President. But the electoral process, including Congress’ role, has so many uncertainties and choke points that applying it is fraught, particularly in this time of hyper-partisanship, social unrest, and economic strife. It would behoove us to consider critical issues – including those endemic in mail-in balloting – well before hand. Once Election Day comes and goes, the electoral calendar is not conducive to a dispassionate, considered, orderly process.