Retired Navy Adm. William McRaven said Sunday that he doesn't think the president-elect can get back into the Iran nuclear deal without some changes.

"There's been a lot of controversy and a lot of folks who don't like the JCPOA and I understand that," McRaven said on ABC's "This Week." "But the fact of the matter is the JCPOA, which probably going to give us, you know, 10 to 12 to 15 years before the Iranians could possibly have enriched enough uranium to build bomb."

Complicating matters is Friday's apparent assassination of one of Iran's most prominent scientists, Mohsen Fakhrizadeh. While no one has claimed responsibility for the killing, the incident has brought out a full response from Iran's top officials, including the country's foreign minister, Mohammad Javad Zarif, who pointed the finger at Israel.

"Now, of course, by attacking their nuclear scientist, by really escalating this effort, the Iranians I think are going to be more compelled to try to get a bomb quicker. This is going to complicate President Biden's efforts, diplomatic efforts," he told "This Week" Co-anchor Martha Raddatz on Sunday. "Now, again, from the Iranian standpoint, after President Trump pulled out of the JCPOA, I think they are going to be very, very reluctant to get into any agreements with the United States at this point. So, a President Biden will have a difficult challenge on his hand."

Another court ruling has gone against allies of the Trump campaign in their bid to halt certification of the 2020 presidential election in Pennsylvania, as the state's Supreme Court issued an order Saturday dismissing a recent court challenge focused on mail-in voting.

This election challenge was brought by U.S. Rep. Mike Kelly, a Republican, along with another GOP candidate for Congress, alleging that the state legislature had not legally passed the measure allowing for universal mail-in voting.

The plaintiffs called on the court to have Pennsylvania Secretary of State Kathy Boockvar cancel all mail-in ballots or, if not, to empower the state legislature to appoint new electors. A trial judge on Tuesday had imposed a temporary injunction to pause the election certification process until the question could be resolved. Boockvar's office brought the matter immediately to the state Supreme Court.

The Pennsylvania Supreme Court vacated the injunction on Saturday and dismissed the case with prejudice, meaning the GOP cannot bring it back.

-ABC News' Matthew Mosk and Alex Hosenball

Biden and his transition team have announced three new members of their COVID-19 advisory board.

After facing criticism for not having any current nurses on the advisory board, the new additions are Jane Hopkins, a registered nurse trained in mental health; Jill Jim, who is an enrolled member of the Navajo Nation and the executive director of the Navajo Nation Department of Health; and David Michaels, an epidemiologist and professor at George Washington University.

This brings the total number of members on the coronavirus advisory board to 16.

“As COVID-19 surges across the country, I need a team advising me and a transition that offers diverse perspectives and viewpoints,” Biden wrote in a statement. “Ms. Hopkins, Dr. Jim, and Dr. Michaels will strengthen the board’s work and help ensure that our COVID-19 planning will address inequities in health outcomes and the workforce.”

The COVID-19 advisory board will help shape the approach to managing the current surge in coronavirus infections as well as ensuring an eventual vaccine is safe and effective, according to Biden’s transition team.

-ABC News’ Beatrice Peterson

Vice President-elect Kamala Harris, her husband Doug Emhoff and Washington D.C. Mayor Muriel Bowser visited a holiday market in the Penn Quarter neighborhood of D.C. for Small Business Saturday.

Harris appeared to be wearing two masks and chatted with a couple of vendors, at one point stopping at a stand and holding up a T-shirt that read “Madam Vice President,” prompting the crowd to cheer.

Harris bought two puzzles at the New York Puzzle Company, which Emhoff paid for as the merchant took a photo of her through the plexiglass barrier.

At Marcella Kriebel Art and Illustration, she eyed a print of different types of coffee. Instead, she picked a print of different kinds of cheeses, while Emhoff bought the “Madam Vice President” T-shirt.

Harris stopped to greet shoppers before speaking with reporters. “We’re here with the great mayor of Washington DC, Muriel Bowser, to celebrate the small businesses that are here, but to celebrate small businesses all over our country. They’re suffering,” she said.

“They are always really part of -- an essential part of the lifeblood of a community, part of the civic and social fabric of a community and, sadly, since COVID started, one in four small businesses in our country has closed,” she added.

Biden tweeted Saturday, “Small businesses are the backbone of communities across the country — and amid the pandemic, they need our help more than ever. Today, and every day, support your neighbors and strengthen your community by shopping small. #SmallBusinessSaturday.”

When asked about Trump and Vice President Pence not participating in the transition, Harris deflected and focused on how she and Biden are going to assist small-businesses during the pandemic.

“We -- and the American people deserve that the incoming administration focuses on what’s important and what is important is getting a handle on this virus, opening back up our small businesses and -- and focusing on -- on the experts in all areas,” she said.

Harris was asked about reports that Trump has expressed a desire to run for president in 2024 and scoffed at the notion.

“Please,” she said, laughing.

-ABC News’ Averi Harper