WASHINGTON — Many states have thousands of mailed military ballots. Many states have tight deadlines for counting them. And many states are swing states. But this year six states stand out for checking all three of those boxes.

In Pennsylvania, Georgia, Arizona, Michigan, Wisconsin and Minnesota, state law provides little or no time after Election Day for military ballots to be counted. If the election is close enough, the outcome in one or more of those states could tilt the national contest one way or the other, and counting those ballots — or not — could determine the outcome.

Several factors could make it harder to count all ballots on time, whether mailed or cast in person. These include postal system delays as well as the sheer number of ballots of all types that are being cast — perhaps the most in U.S. history.

“These military ballots could indeed be pivotal,” said Susan Dzieduszycka-Suinat, president and CEO of Overseas Vote, an advocacy initiative of the nonprofit U.S. Vote Foundation. “Even one military ballot not counted is a loss to our nation. I see it as shameful and a lost opportunity for legislators and courts to be tightening up the ballot-receiving deadlines for military voters.”

A Military Times-Syracuse University poll this summer found that former Vice President Joe Biden had a four-point lead over President Donald Trump among surveyed military troops, typically considered a demographic that skews Republican.

FILE – In this Thursday, Sept. 3, 2020, file photo, stacks of ballot envelopes waiting to be mailed are seen at the Wake County Board of Elections in Raleigh, N.C. Time was dwindling for thousands of North Carolina voters to fix absentee voting errors as elections officials hustled out an updated process for handling mail-in ballot problems two weeks before Election Day. (AP Photo/Gerry Broome, File)

Contrary to what Trump has said, in every election, many states are still counting mailed-in ballots after Election Day. Even with the final count unfinished, media organizations in most cases can predict the outcome on the night of the election because the number of mailed-in ballots usually is not enough to decide the contest.

But excruciatingly tight races are not unheard of. In Florida in 2000, George W. Bush defeated Al Gore by just 537 votes.

In 2020, if the presidential contest turns out to be close, Pennsylvania could be the fulcrum on which it turns.

The Supreme Court ruled on Oct. 28 that the Keystone State can count votes received up to three days after the Nov. 3 election. The state’s election officials say they are setting those ballots aside to be counted later, if necessary.

Trump, anticipating the possibility that he will be ahead in Pennsylvania on election night, said over the weekend that he plans to sue to prevent the counting of those additional Pennsylvania ballots after Nov. 3.

Once the polls close Tuesday, Trump said, “we’re going in with our lawyers.”

In the 2016 election, 7,788 overseas military and civilian ballots were received in Pennsylvania, according to the U.S. Election Assistance Commission’s report on that contest. This year’s tally of mailed overseas ballots is expected to be higher both in Pennsylvania and elsewhere, experts said.

Depending on when those absentee Pennsylvania ballots are received — and the outcome of possible court cases triggered by Trump — some of the votes may never be counted.

Pennsylvania is not the only swing state with thousands of military mail ballots and tight deadlines for counting them.

Arizona and Michigan, two states considered pivotal in the presidential election, each had nearly 5,000 overseas mail votes in 2016 — and they will probably see more such ballots in 2020.

Those two states do not count any mailed overseas ballots received after Election Day, even if they are postmarked by then, according to a report last month by Count Every Hero, an advocacy group for military voters.

Georgia, another swing state, which also had just over 5,000 overseas mail ballots in 2016, only allows until Nov. 6 to receive those mailed ballots, the report said.

Wisconsin and Minnesota each received about 3,000 military absentee ballots in 2016, with more expected this year. Courts have ruled in recent weeks that postal ballots received after Election Day cannot be counted in either of those swing states, even though voters had been told otherwise.

In fact, 22 states still do not allow such absentee ballots to be counted if they are received after Election Day, according to Count Every Hero.

Military personnel have voted in elections dating back to the War of 1812 and in large numbers since the Civil War.

The modern system of absentee ballots for military and overseas personnel was set up in 1986 under the Uniformed and Overseas Citizens Absentee Voting Act (PL 99-410). It applies not just to troops deployed overseas and diplomats but also to military personnel who are located anywhere outside their permanent state of residence, including in the United States, when they need to vote.

In 2009, Congress enacted an update in the defense authorization law called the Military and Overseas Voter Empowerment Act. It required that ballots be sent out 45 days before an election and permitted much of the process to happen electronically.

In the 2016 election, more than 600,000 overseas and military ballots were received, according to the election commission’s survey.

In 23 states, military personnel and overseas civilians can vote online, and substantial portions of them do, according to Dzieduszycka-Suinat of Overseas Vote.

But thousands of absentee military paper ballots also still come in. It is unacceptable, advocates said, if such ballots are kept from affecting tight races in key states for want of a few days reprieve from a deadline. It is also intolerable on principle, many have said.

Scott Cooper, a retired Marine Corps officer who works with Count Every Hero, points out that Trump was ahead in the popular vote at midnight on Election Day in 2016. Yet he ultimately netted nearly 3 million fewer votes than Hillary Clinton.

“That’s not stealing the election, that’s making sure that everybody’s vote counts,” Cooper said. “Those in uniform who are wearing the cloth of the nation are among those votes that count.”