So far, officials in Mr. Trump’s government have worked in good faith, according to Biden officials, who said they hoped and expected that cooperation to continue.

As coronavirus infections hit new highs, Mr. Biden’s aides are planning for the first critical transition decisions to focus on health care and addressing the pandemic, the central theme of his campaign in the final months. They have assembled an internal group of roughly two dozen health policy and technology experts to look at the development and delivery of a vaccine, improving health data and securing supply chains, among other issues…

Parts of the cast that had Mr. Biden’s ear throughout the presidential campaign — Anita Dunn, a senior adviser; Steve Ricchetti, another former vice-presidential chief of staff; and Mr. Klain — are among those guiding the formation of a would-be government. Senator Kamala Harris of California, his running mate, is generating names and speaks regularly to Mr. Biden. In Mr. Biden’s policy orbit on the campaign, Jake Sullivan and Antony J. Blinken are widely seen as the most influential figures, and both are expected to hold senior posts in a potential administration.