The president was back Sunday at Trump International Golf Club in Sterling, Virginia. Trump was also there on Saturday when ABC News characterized Biden as the apparent winner in Pennsylvania, giving the former vice president the electoral votes he needs to capture the presidency.

Pennsylvania Attorney General Josh Shapiro has informed the Supreme Court that, contrary to Republican concerns, all of the state's counties have been complying with the Secretary of State's guidance to segregate late-arriving mail ballots.

"At the time Secretary of the Commonwealth Kathy Boockvar filed her Response in Application to the Republican Party of Pennsylvania’s Emergency Application for Injunction earlier yesterday, 63 of Pennsylvania’s counties had affirmatively confirmed their understanding and intention to follow the Secretary’s October 28, 2020 and November 1, 2020 guidance, as noted in the Response," he wrote. "The Office of the Secretary of the Commonwealth has confirmed that the remaining four Pennsylvania counties have similarly confirmed their understanding and intention to follow that guidance. We would appreciate if you would circulate copies of this letter to the Justices of the Court. "

Shapiro seems to suggest that Justice Samuel Alito's order late Friday was not necessary given that the counties were already doing the segregation, notwithstanding the unfounded GOP speculation that they might not have been.

-ABC News Senior Washington Reporter Devin Dwyer

Former President George W. Bush said in a statement that he spoke with Biden and congratulated him on the outcome of the 2020 presidential election.

Bush said in the statement that he also spoke with Kamala Harris, who he congratulated for “her historic election to the vice presidency.”

“Though we have political differences, I know Joe Biden to be a good man, who has won this opportunity to lead and unify our country,” the statement read.

On Sunday, several more world leaders, such as South Korean President Moon Jae-in, the Saudi royal family and Israeli Prime Minister Benjamin Netanyahu, also congratulated Biden on his apparent win.

Ahead of Election Day in the United States, the biggest question for Iran was the future of the Iran nuclear deal, formally known as the Joint Comprehensive Plan of Action. The current Iranian government, led by President Hassan Rouhani and his Foreign Minister Mohammad Javad Zarif, have indicated they are willing to revive the deal and assemble the current signatories to negotiate a new agreement.

Looking ahead to a Biden administration, Rouhani said Sunday, "the next U.S. administration should use the opportunity to make up for the past mistakes against Iran."

Iran's semi-official Fars News Agency reported that just the day before, Rouhani expressed hope that the new administration would rejoin the nuclear deal.

Rouhani said the Iranian people faced "economic terrorism" in the past three years and showed "competent resistance and patience."

He said Iran will continue its "patience" and "resistance."

“We hope that conditions alter in a way that those who have imposed sanctions will come to realize that they have moved along a wrong path, and that they will not attain their goals at all as they should take a lesson from this 3-year experience," he continued.

-ABC News' Christine Theodorou

Biden warns of 'dark winter' ahead as he lays out COVID-19 plan, calls for unity on masks

President-elect Joe Biden in his first solo remarks to Americans since his victory speech over the weekend reminded Americans of the ongoing coronavirus pandemic as cases and hospitalizations rise across the country, and said the country is “still facing a very dark winter” before offering his plan to combat it.

"We are ready to get to work addressing the needs of the American people. Today, that work begins," Biden said from The Queen Theater in Wilmington Delaware, following a briefing with his newly-announced COVID-19 advisory board. "It starts with doing everything possible to get the COVID-19 under control, so that we can reopen our businesses safely and sustainably, resume our lives, put this pandemic behind us."

While he praised the announcement from Pfizer Monday morning that the company has a vaccine in trial that looks "90% effective in preventing COVID-19," Biden reminded that even if the vaccine is approved, it will not be widely available for months. He went on to urge all Americans, regardless of whether they voted for him, to "end the politicization of basic responsible public health steps."

"This election is over. It’s time to put aside the partisanship and the rhetoric that’s designed to demonize one another," Biden said, reminding Americans to keep social distancing and wearing a mask.

"Doesn't matter who you voted for, whether you stood, where you stood before election day, doesn't matter your party, your point of view. We can save tens of thousands of lives if everyone would just wear a mask for the next few months. Not Democrat or Republican lives, American lives," he added. "A mask is not a political statement but it is a good way to start pulling the country together."

After pledging to rejoin the World Health Organization on "Day One," Biden also said his advisory board will include experts on global health security, "so that we can restore U.S. global leadership to fight this pandemic" -- in sharp contrast to Trump's isolationist approach to the virus and general policy.