Officials in Michigan and Pennsylvania are slated to meet Monday to certify votes despite last-ditch efforts by Trump and his allies to override his election loss through legal battles and political pressure on GOP-controlled state legislators.

The president has largely hunkered down inside the White House since Election Day -- the last time he took questions from reporters -- and has no public events on his schedule again Monday. Over the weekend, as coronavirus cases climbed across the country, Trump went golfing instead of meeting with world leaders at a G20 event about the pandemic.

Biden and Harris are pressing forward with their transition, meeting virtually with the U.S. Conference of Mayors, a nonpartisan organization, on Monday.

Biden’s team, meanwhile, continues to warn that Trump's refusal to concede not only harms American democracy but, hindering their access to pandemic plans, may put American lives at risk.

Ron Klain, Biden's incoming chief of staff, told ABC’s “This Week” that the president-elect is still being denied intelligence briefings, FBI background checks on potential Cabinet nominees and access to agency officials to help develop plans including those on coronavirus vaccine distribution.

Biden shared a congratulatory phone call Sunday night with Prime Minister Jacinda Ardern of New Zealand, according to a readout issued by his transition team.

Biden also congratulated Ardern on her reelection, which she overwhelmingly won last month, and the two discussed containing COVID-19, climate change, strengthening democracy and "maintaining a secure and prosperous Indo-Pacific region."

The president-elect also praised Ardern's leadership after the 2019 Christchurch massacre and during the COVID-19 pandemic, calling her a "role model."

In total, Biden has now spoken with world leaders from 14 different countries and the Vatican.

-ABC News’ John Verhovek

With less than 60 days until the inauguration, the Trump administration is still refusing to recognize Biden as the president-elect as a small but growing number of Republicans are calling for a full and formal transition process to begin.

Republican Sen. Lisa Murkowski of Alaska was the latest to add her voice, slamming Trump’s apparent “pressure campaign” on state legislators to try to overturn election results as “unprecedented” and “inconsistent with our Democratic process” while calling for Biden’s ascertainment in a statement Sunday.

Former New Jersey Gov. Chris Christie, a close confidant of Trump’s who helped him prepare for debates, called his legal team “a national embarrassment” on ABC’s “This Week” following another defeat in a Pennsylvania court over the weekend with a blistering dismissal from the judge.

After the ruling, Republican Sen. Pat Toomey of Pennsylvania urged Trump to concede the loss and facilitate the transition process, suggesting that his legacy will be harmed if he doesn’t help unify the country.

Republican Gov. Larry Hogan of Maryland, who has publicly feuded with Trump over the federal government’s response to COVID-19, also said Sunday he was more “embarrassed” by others in the party who haven’t spoken out.

Liz Cheney, chair of the House Republican Conference, also asked Trump over the weekend to respect "the sanctity of our electoral process" if he can’t prove his claims of widespread voter fraud, which he’s so far been unable to do.

Even Trump allies like Sen. John Cornyn, R-Texas, are calling on the Trump administration to give Biden intelligence briefings -- even if they aren’t publicly recognizing him yet as the president-elect.

Biden is expected to name Linda Thomas Greenfield as his pick for U.S. ambassador to the U.N., according to two sources familiar with the matter.

Greenfield, a retired foreign service officer, is currently leading the State Department agency review team for the Biden transition and was one of the officials who briefed him last week on national security.

She would be just the second Black woman to ever serve in the post.

Biden's transition declined to comment to ABC News.

-ABC News' Conor Finngean, Benjamin Siegel and John Santucci