The new moratorium was not identical to the earlier one, which had applied nationwide. It was instead tailored to counties where Covid-19 was strongest, a category that currently covers some 90 percent of counties in the United States.

Mr. Biden was frank in discussing his reasoning, saying the new measure faced long odds but would buy tenants some time.

“The bulk of the constitutional scholarship says that it’s not likely to pass constitutional muster,” he said on Aug. 3. “But there are several key scholars who think that it may — and it’s worth the effort.”

Two days later, he offered further thoughts.

“Here’s the deal,” he said. “I can’t guarantee you the court won’t rule if we don’t have that authority, but at least we’ll have the ability, if we have to appeal, to keep this going for a month at least — I hope longer than that.”

The moratoriums deferred but did not cancel the obligation to pay rent, but the challengers wrote that this “massive wealth transfer” would “never be fully undone.” Many renters, they wrote, would be unable to pay what they owed. “In reality,” they wrote, “the eviction moratorium has become an instrument of economic policy rather than of disease control.”

Even before the Supreme Court ruling, data released by the Census Bureau on Wednesday estimated that 1.2 million households were very likely to face eviction for nonpayment of rent over the next two months.

Still, many states and localities, including New York and California, have extended their own moratoriums, providing another layer of protection for some renters. In some places, judges, aware of the potential for large numbers of people to be put out on the street even as the pandemic intensifies again, have said they would slow-walk cases and make greater use of eviction diversion programs.

Glenn Thrush contributed reporting.