While some outcomes -- like a convincing victory by either candidate -- could render a legal fight pointless, the president has been increasingly vocal about his intention to challenge a narrow win by his opponent.
"We're going to go in the night of, as soon as that election is over, we're going in with our lawyers," Trump told reporters Sunday.
But just how and where the presidential contest could be thrown to judges may depend most on where the vote on Tuesday is the closest. Trump's strategy, legal observers told ABC News, appears designed to remain flexible so that the campaign's attorneys can zero in on contests where a legal challenge could have a greater chance of flipping a state to the president's favor.
"Judging from the public statements that the president has made, there is perhaps more than one strategy that they're contemplating," said Wendy Weiser, who directs the Democracy Program at the Brennan Center for Justice at NYU School of Law. "They're in a lot of places right now. Some of it is, throw everything against the wall and see what sticks."
Weiser said the arguments the Trump legal team has mounted in more than 40 cases around the country ahead of the 2020 elections mostly boil down to two central legal questions -- either one of which could help carry a case to the U.S. Supreme Court.
In the first, which was featured prominently in litigation in Pennsylvania, Republicans argued that any effort by elections officials to expand voting opportunities would increase the risk of fraud, and that increased risk infringes on the rights of other voters. Trump lawyers have lost the cases testing this theory, in part because they have been unable to offer evidence of fraud or a risk of fraud, Weiser said.
The second argument questions many of the changes to accommodate voting during the coronavirus pandemic because they were made by state elections officials or governors, and not by state legislatures. The U.S. Constitution assigns the task of laying out election rules specifically to state legislatures. This argument has gained currency with several of the conservative-leaning U.S. Supreme Court justices, and could resurface before them, Weiser said.
Weiser called it "absurd" that the courts would require state officials to get state legislative approval for every aspect of carrying out an election. "That's contrary to the entire thrust of American law," she said.
Here are the court challenges in critical states that could make the difference:
The Trump campaign and Republicans are poised to mount a challenge in Pennsylvania to the validity of mailed-in absentee ballots postmarked before Tuesday but received up to three days after the election, an extension granted by the state Supreme Court.
The Supreme Court rejected Republicans' requests to consider the matter before the election, but four justices signaled a willingness to reconsider after Tuesday. The Pennsylvania Supreme Court initially granted the extension, but this was a case where Republicans argued the court was beyond its purview to do so -- that the matter should have been left to the state legislature.
This election cycle, Trump has repeatedly denounced the idea of counting votes after Election Day -- a standard practice every four years -- but it's unclear what legal mechanism he could use to make that argument since the Constitution leaves the conduct of elections to the states.
Separately, the Trump campaign has challenged 237 mail-in ballot applications in Allegheny County, the state's second largest county, which includes Pittsburgh, an urban center that tends to favor Democrats. But they did not do the same in Philadelphia, or any other counties by Friday's deadline, according to Kathy Boockvar, the state's top election official. So far, state officials have accepted more than 2.4 million mail-in ballots.
A judge on Monday denied the Trump campaign's petition in Clark County, Nevada, to stop counting mail-in ballots because it argued that the process wasn't robust enough. Statewide, more than half-a-million Nevada voters have mailed in ballots, and mail-in voting has more than doubled the numbers from 2016.
The Trump campaign, which brought the lawsuit in Democratic-stronghold Clark County, alleged that the signature matching machines have too high of a match rate, that there is not enough public observation opportunity, and ballots are being handled improperly.
"No evidence was presented that the setting used by Clark County causes or has resulted in any fraudulent ballot being validated or any valid ballot invalidated," District Judge James Wilson Jr. wrote.
Myrna Pérez, director of the Brennan Center's Voting Rights and Elections Program, said voter rights advocates have found that signature matching can too often disenfranchise people.
Clark County, Nevada, has been a particular target of the Trump campaign because high turnout in that county essentially guarantees a Democratic win statewide, especially in this tight race.
The lawsuit was one of two the Trump campaign brought there in recent weeks. The second involves a massive public records request to allow the Trump campaign to conduct their own review of a voters' signatures on file with the department of motor vehicles so they can compare them to cast ballots.
The Nevada Independent reported Tuesday that a judge had issued a short written order partially granting a limited portion of the requested records related to the county's ballot counting and verification procedures, but rejecting a host of other requests as invasive or made improperly. None of the information needs to be made available until after the election canvas in the state is complete, however, because the judge ruled that clerks have too much on their hands.
Michigan officials have warned that they do not expect to have complete results on election night -- or a winner, if the race is tight-- because of the influx of mail in ballots this year.
Instead, they have vowed to count every single one of them, even if challenges arise.
"Any effort to discount over half of all votes in our state is nothing short of a coup," Michigan Attorney General Dana Nessel tweeted on Tuesday in response to Trump's comment that he would send in lawyers when Election Day is over. "The Michigan Department of Attorney General will be ready to counter any such effort."
Nearly 3 million absentee ballots have already been cast in the state.
Earlier this month, a Michigan Court of Appeals blocked a two-week absentee ballots extension that was granted earlier this fall -- a loss for Democrats in the state on an issue that has become the center point for litigation in battleground states around the country. Ballots must now arrive by Election Day.
The focus of lawsuits in North Carolina has been changes to the rules for mail-in absentee ballots. Last week, the U.S. Supreme Court denied a Republican effort to block changes that allowed the acceptance of any ballot postmarked by Nov. 3. That means North Carolina's State Board of Election will accept ballots mailed on time, even if they are received up to Nov. 12.
A close race could lead to renewed challenges of the rule change, which the board made in late September citing the coronavirus. North Carolina Senate Leader Phil Berger, a Republican, filed one of the Supreme Court appeals. A spokesperson for Berger told ABC News the potential for litigation is not unusual with any election but there is a heightened probability this year because courts were still debating the deadlines even after voting had already begun.
"The [state election] board's actions we think are unfortunate because it just increases the possibility of litigation. There's a lot more uncertainty because those rule changes that happened after balloting already began," said Pat Ryan, Sen. Berger's deputy chief of staff. "I think everybody hopes that the results are such that there is no need for litigation because the results are so clear."
In Texas on Monday, a federal judge rejected a Republican effort to invalidate roughly 127,000 drive-thru votes cast in Harris County, Texas, saying he believes the plaintiffs who brought the case did not have standing to sue.
But Judge Andrew Hanen, an appointee of President George W. Bush, ordered Harris County to maintain records regarding all of its drive-thru votes in the event the case was appealed successfully. Hanen added that if the Fifth Circuit reversed his ruling and said that plaintiffs did have standing to sue and the matter was sent back to him, he still would not invalidate the votes already cast at drive-thru sites.
The case is one of several in Texas that has raised the ire of Democrats, who argued that the accommodations made for voters had been approved by local officials and that individuals should not see their ballots thrown out. Texas Democratic Party Chair Gilberto Hinojosa said following the ruling that he thought the Trump campaign was abusing the legal system to suppress legitimate support for his opponent.
"Texans who lawfully voted at drive-thru locations should have never had to fear that their votes wouldn't be counted and their voices wouldn't be heard," Hinojosa said. "This lawsuit was shameful and it should have never seen the light of day."
Georgia Secretary of State Brad Raffensperger said Monday that state officials are expecting legal challenges following the election.
"We anticipate that in any situation where we have a close election like this in what is now viewed as a swing state, there's going to be challenges," Raffensperger. "There'll be challenges from Republicans. There'll be challenges from Democrats, and we expect them all to be going into court more than likely."
Raffensperger said he had no way to know what specific concern issue might lead to a court challenge, but said it was safe to "anticipate that there will likely be some kind of lawsuit some kind of challenge, somewhere."
ABC News' Quinn Scanlan and John Santucci contributed to this report.