Hillary Clinton issued a warning for Democratic presidential candidate Joe Biden in a new interview released Tuesday, urging the former vice president to not concede defeat on the night of the Nov. 3 election — no matter the circumstances.

"Joe Biden should not concede under any circumstances," Clinton said. "Because I think this is going to drag out, and eventually, I do believe he will win, if we don't give an inch and if we are as focused and relentless as the other side is."

Clinton, the 2016 Democratic nominee, lost the presidential election four years ago to President Trump. An aggregate of polls by RealClearPolitics shows Biden leading Trump, a Republican, by more than 7 percentage points nationally.

But Clinton suggested the election will be "close," accusing Republicans of trying to tamper with the results by "messing up absentee balloting" to secure a narrow advantage in the Electoral College.

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"We've got to have a massive legal operation," she said. "And I know the Biden campaign is working on that."

Clinton, a former secretary of state under then-President Barack Obama, made the remarks during an interview on Showtime’s “The Circus," part of which was released Tuesday.

Millions of Americans are expected to vote by mail this November due to the coronavirus pandemic, increasing the chances the winner of the presidential race won't immediately be known on election night. State election officials in several key battleground states have warned it could take days to count the votes, given the influx of absentee and mail-in ballots they expect to receive.

The result has been a partisan battle over voting by mail, exacerbated by fears among some Democrats over operational changes implemented at the U.S. Postal Service by Postmaster General Louis DeJoy, a longtime Republican fundraiser.

DeJoy approved changes to the agency aimed at cutting costs, including prohibiting overtime, shutting down sorting machines early and requiring carriers to leave mail behind when necessary to avoid extra trips or late delivery on routes. But he's since reversed course, saying the changes to the Postal Service will be suspended until after the November election.

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Democratic leaders have accused the White House of trying to hamper mail delivery and suppress votes.

House Speaker Nancy Pelosi said at the end of July that Trump's attacks on voting by mail are part of a broader effort to sow confusion and suppress voter turnout for the election.

"The reason he does it is because the more people hear something like that, the more they're discouraged to vote," Pelosi said during an interview with CNN's Brianna Keilar. "It's a way to suppress the vote."

Obama echoed that sentiment in a tweet in mid-August.

"Everyone depends on the USPS. Seniors for their Social Security, veterans for their prescriptions, small businesses trying to keep their doors open," Obama wrote. "They can't be collateral damage for an administration more concerned with suppressing the vote than suppressing a virus."

Trump has repeatedly raised concerns of fraud involving mail-in voting, a fear that he reignited on Monday during the first night of the Republican National Convention.

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"What they’re doing is using COVID to steal an election," Trump said. "They’re using COVID to defraud the American people, all of our people, of a fair and free election. We can’t do that."

So far, nine states — a majority of which are run by Democratic governors — have said they intend to mail ballots to all voters.