The Supreme Court has denied a GOP request to block a six-day extension of the mail ballot deadline in North Carolina which was imposed by the state board of elections.

The decision was 5-3, with Chief Justice John Roberts and Justice Brett Kavanaugh joining the liberal justices. Justices Clarence Thomas, Samuel Alito and Neil Gorsuch would have granted an emergency injunction.

"Such last-minute changes by largely unaccountable bodies invite confusion, risk altering election outcomes, and in the process threaten voter confidence in the results," Gorsuch wrote in the dissent.

Justice Amy Coney Barrett took no part in the decision, the court said, because "of the need for a prompt resolution and because she has not had time to fully review the parties’ filings."

-ABC News Senior Washington Reporter Devin Dwyer

National Guardsmen will be called up in some states on Election Day as election workers or to facilitate the opening of polling places to help make up for shortfalls of poll workers as a result of the coronavirus pandemic.

Voters won't know that they are National Guardsmen, however because they're being called to active duty to serve as state government employees helping out on Election Day, so they won't be wearing uniforms or carrying weapons.

Behind the scenes, National Guard cyber units have helped with the security of state computer systems and will be able to help out state IT teams if there are issues on Election Day.

Wisconsin and Tennessee will have National Guardsmen helping out at polling centers. In Wisconsin they'll be working as poll workers and helping with cleaning and providing sanitary supplies to the locations. Guardsmen in Tennessee are not allowed to serve as poll workers, so they'll be facilitating the opening of polling centers.

Nebraska's Maj. Gen. Daryl Bohac reiterated that guardsmen helping out as poll workers will essentially be civilians and if there's a need for security assistance because of violence or a threat of violence, they'll be calling 911 for law enforcement assistance, just like any other civilian.

In Washington state, "the biggest thing they're looking at is potential intrusion into the system. So looking at firewalls, looking at the status of the Vote Washington system," said Brig. Gen. Gent Welsh, Washington's Assistant Adjutant General. "Looking for anomalies in the system, basically typical network hygiene that you would usually expect to see anywhere and in a company, or even in the military."

Washington state is a vote-by-mail state, so on Election Day, Welsh said five guardsmen will be part of the team ensuring that the tabulation of votes is safe. They've been there for the past month preparing for Election Day and they'll remain on duty for four to five days after that to ensure the system's security. Welsh said cyber teams first started working on assessing vulnerabilities to the state's systems. "Most all of it is done over the shoulder of the Secretary of State teams, their own IT staff, teach them how to do these things as well. But again, just another extra set of eyes," he said.

In Tennessee, 30 Guardsmen have been providing "subject matter expertise" ensuring the counties have a "very robust support system" as they upgrade their software and assist with "the basic protocols of insurance," said Maj. Gen. Jeff Holmes, Tennessee's adjutant general. He said that six or seven counties had asked for specific assistance.

Wisconsin's assistant adjutant general, Brig. Gen. Robyn Blader, also added that, "the extent of Wisconsin National Guard's role in the November election, is still being determined."

-ABC News' Luis Martinez

The Supreme Court has rejected Pennsylvania Republicans' second attempt to block an extended deadline for mail-in ballots for the 2020 election.

The high court announced the 5-3 decision Wednesday evening that it will not expedite a Republican request to stop the state's extended deadline for receiving mail-in ballots, a small and potentially temporary victory for Democrats who believe mail-in ballots in the battleground state could determine the election.

Justice Amy Coney Barrett did not participate in the case "because of the need for a prompt resolution of it and because she has not had time to fully review the parties' filings," the court's spokeswoman said.

The court's order did leave open the possibility that the justices could take up the measure again and decide after voting whether a three-day extension to receive and count absentee ballots ordered by the state's high court was proper. The decision leaves open a potential question as to the validity of any ballots received after Election Day.

Justice Samuel Alito, writing for the three dissenting justices -- himself, Justice Neil Gorsuch and Justice Clarence Thomas -- indicated he would support the court's eventual review of the issue but wrote, "I reluctantly conclude that there is simply not enough time at this late date to decide the question before the election."

Earlier in the month, the Supreme Court deadlocked 4-4 on whether to block the extension -- effectively leaving in place a Pennsylvania Supreme Court decision that mandated the extension. Republicans were hoping Barrett's place on the court could produce a different outcome. In the end, Justice Brett Kavanuagh joined the majority in this decision.

Experts say due to the expected record amount of mail-in voting, election night could be more like election week, but Trump said earlier in the day he expects the courts would "hopefully" block any ballot deadline extensions.

Democrats on the House Oversight Committee have released new data from the Postal Service on delivery rates -- saying that it shows that Postmaster General Louis DeJoy has failed to address concerns about the speed of deliveries raised at his congressional testimony this summer.

With just six days until Nov. 3, House Democrats are also urging voters to avoid relying on the Postal Service to return their ballots and to instead vote in-person or use drop boxes.

"At this point, Americans should either vote in person or drop their ballot in an official drop box to avoid their ballots not being delivered on time," Rep. Carolyn Maloney, D-N.Y., the chair of the panel, and Rep. Gerry Connolly, D-Va., said in a statement. "The latest Postal Service data confirms our fears that Postmaster General DeJoy's reckless and unexamined changes undoubtedly resulted in service disruptions right before the election."

-ABC News' Benjamin Siegel