WILMINGTON, Del. — President Trump will be remembered as one of the nation's most reckless leaders for holding up cooperation on the deadly coronavirus pandemic after losing his bid for reelection, President-elect Joe Biden said Thursday.

At the White House, Vice President Pence tried to apply a veneer of calm to a tumultuous outgoing administration as he and federal health officials held what has become a rare public discussion of the federal government’s efforts to address the pandemic.

In Wilmington and in Washington on Thursday, the two events provided a split screen of sorts illuminating the challenges confronting the incoming administration on the most immediate crisis it faces. The events also showed the extent to which the Trump administration is ignoring the reality that in just two months there will be a change of power at the White House.

Trump’s refusal to concede his election loss and allow his government to share information with the incoming Biden administration will “put us behind the eight ball” for a month or more after taking office, and just as lifesaving vaccines are expected to be distributed, Biden said.

“And that’s lives. How many will be lost as a consequence of that?” the president-elect said during a news conference here. “I can’t tell you.”

Meanwhile, Pence and public health officials touted encouraging news on vaccines, particularly on their efficacy, and promised Americans that millions of doses could be distributed almost immediately upon approval of a vaccine by the Food and Drug Administration. They urged the country to continue mitigation measures such as wearing masks and social distancing — even as Pence did not wear a face covering at the White House podium.
Biden removed his face mask when he spoke at a podium inside the Queen Theater, but wore it as he entered and left the venue.

The vice president, who ignored a cacophony of shouted questions from reporters, even as Biden took questions after his own event in Delaware, also relayed a message from Trump, who has nearly vanished from public view since losing the presidency this month.

“President Trump wanted me to make clear that our task force, this administration and our president does not support another national lockdown, and we do not support closing schools,” Pence said.

Biden’s assessment that Trump would be judged harshly was an apparent appeal to Trump’s vanity and his desire for a positive legacy after becoming the first president since George H.W. Bush to lose reelection. The president-elect said he wanted to “choose my words” carefully, but his message was blunt.

Asked about Trump’s efforts to overturn or undermine Biden’s election victory in Michigan, including an apparent pressure campaign directed at Republican election officials in the Detroit area, Biden called it “another incident where he will go down in history as being one of the most irresponsible presidents in American history.”

Trump has also invited Michigan lawmakers to the White House on Friday as part of a legal and public relations campaign that Biden said is futile, damaging and possibly illegal.

“It’s going to be interesting who shows up,” Biden said, as he predicted that Republicans are tiring of Trump’s antics and are ready to move on.

That is especially true of Republican governors who must figure out how to handle a devastating rise in coronavirus infections, hospitalizations and deaths, Biden said.

The dueling coronavirus events in Wilmington and Washington came as Biden’s transition team continued to be denied access to government officials who could help the incoming administration get up to speed on the federal agencies’ ongoing pandemic response efforts.

But in a private telephone briefing with both Republican and Democratic senators earlier Thursday, the leaders of Operation Warp Speed — the Trump administration’s primary vaccine apparatus — said they had not been asked to brief Biden officials on their efforts, according to multiple officials directly familiar with the call.

The officials — Gustave Perna and Moncef Slaoui — indicated they would communicate with the Biden team if asked, noting they would indeed want the new administration to be prepared, according to people who spoke on the condition of anonymity to discuss a private call.

After a Democratic senator asked vaccine officials about attempts to brief Biden’s team, Sen. John Barrasso (R-Wyo.) asked whether Vice President-elect Kamala D. Harris, a sitting senator, was on the line and invited her to ask a question, according to another person with knowledge of the conference call.

After the operator noted that Harris (D-Calif.) was not on the call, Barrasso — a member of Republican leadership who helped moderate the call — moved on to the next question.

On the call, Perna and Slaoui also relayed to senators an optimistic update on a coronavirus vaccine, saying that the administration expects 20 million people to be vaccinated by the end of December, and that there are enough doses in production for 25 million more people to be inoculated in both January and February, the officials said. The federal government would allocate the vaccines to individual states, which would then carry out their own distribution plans.

Back in Wilmington, Biden spoke after an on-screen meeting with a bipartisan group of governors aimed at assessing the needs of states ahead of Biden’s inauguration in January. Biden’s lead coronavirus advisers and Harris also participated.

The session included the Republican governors of Utah, Maryland and other states that have recently imposed or reimposed tighter pandemic restrictions. Democrats included New York Gov. Andrew M. Cuomo, chairman of the National Governors Association and a frequent target for ridicule from Trump over stringent pandemic controls.

The remarks came as the Centers for Disease Control and Prevention on Thursday recommended against traveling for the Thanksgiving holiday, urging Americans to consider celebrating in their own households instead.

Agency officials said they were alarmed to see 1 million new cases reported across the United States within the past week. They spoke of the risks of travel and gatherings in stark terms, warning that as families get together over the holidays, they could inadvertently bring the deadly disease with them.

The Thanksgiving holiday comes as coronavirus cases have skyrocketed across the United States, with the seven-day average of new cases hovering at more than 160,000 on Thursday, according to Washington Post tracking. The nation’s death toll since the start of the pandemic reached 250,000 on Thursday. On Wednesday, nearly 1,900 deaths were reported, marking the deadliest day since May.

At the White House, Pence and other health officials echoed the alarm about the rise in cases.

“We’re talking about intensifying” basic public health measures, said Anthony S. Fauci, the top infectious-disease official. “If you’re fighting a battle . . . you don’t stop shooting. You keep going until the cavalry gets here.”

It’s unclear what other immediate relief may be coming for millions of Americans grappling with the health and economic consequences of the coronavirus pandemic.

Top aides for the “Big Four” congressional leaders — House Speaker Nancy Pelosi (D-Calif.), Senate Majority Leader Mitch McConnell (R-Ky.), Senate Minority Leader Charles E. Schumer (D-N.Y.) and House Minority Leader Kevin McCarthy (R-Calif.) — met earlier Thursday to begin discussing the contours of the must-pass year-end spending package to keep the government operating, according to Hill officials.

The spending discussions are likely to include some coronavirus relief provisions that could pass in tandem with the funding bill, although Republican aides stressed that Thursday’s meeting was not about negotiating a separate, large stimulus package. Active discussions on a bill focused primarily on coronavirus relief have stalled for now.

Pelosi, Schumer, Biden and Harris will gather in Wilmington on Friday for their first in-person sit-down since the Nov. 3 election. The agenda for the meeting was not immediately clear.

Also on Thursday, Biden said he has selected someone to be nominated as the next Treasury Department chief, though he did not reveal the name. The pick will be a consensus choice for all wings of the Democratic Party, Biden said, and will be announced soon — either shortly before or after Thanksgiving.