Optimism about the economy has taken a nosedive among Republicans. But the economy did not drive the change. The presidential election did.

After President Trump’s loss to former Vice President Joseph R. Biden Jr., more than 40 percent of Republicans who were polled for The New York Times said they expected their family to be worse off financially in a year’s time, up from 4 percent in October. Democrats expressed a rise in optimism — though not as sharp as the change in Republican sentiment.

The new polling, by the online research firm SurveyMonkey, reaffirms the degree to which Americans’ confidence in the economy’s path has become entwined with partisanship and ideology. In the days after the election, for the first time since Mr. Trump took office in 2017, Democrats and independent voters expressed higher levels of confidence in the economy than Republicans did.

Democrats in November were nearly three times as likely as they were in October to say they expected good or very good business conditions in the country over the next year. They were more than twice as likely as they were in October to say they expected “continuous good times economically over the next five years.”

Republicans were actually more likely to say that they were doing well in November, compared to October. But nearly three in four said they expected “periods of widespread unemployment or depression” in the next several years, up from three in 10 in October.

Nancy Veits, a Republican voter in Los Angeles County, said the economy was a major factor in her decision to vote for Mr. Trump. A retired small-business owner, Ms. Veits, 81, said that she appreciated the president’s commitment to deregulation — and that she feared for the economy after his departure.

“The economy was working,” she said. “I think that under Biden it’s going to be more difficult.”

David Keyston, a survey respondent in Waco, Texas, has a similar set of concerns. He runs his own nonprofit business distributing books about alternative health and healing. Business was good before the pandemic, he said, and has actually improved since the virus began to spread.

Mr. Keyston, 66, said that he didn’t like Mr. Trump’s penchant for Twitter or his demeanor in office. But he said he liked many of Mr. Trump’s policies, like his tax cuts and his promise to build a border wall and to keep the United States out of wars. And he said Mr. Trump had managed the economy well both before and during the pandemic.

“I think he’s tried under the circumstances to do the best he can to maintain some level of economic stability,” he said.

Now, Mr. Keyston’s outlook has turned more dour. He worries that Mr. Biden will impose new restrictions that will cripple the economy, including a nationwide lockdown, a charge that Mr. Trump repeatedly leveled against Mr. Biden, though Mr. Biden did not call for such a lockdown.

“A lockdown will kill this country,” Mr. Keyston said.

Big partisan shifts in confidence have become common following elections in recent decades. Republicans’ economic sentiment fell when Barack Obama was elected president in 2008, then soared when Mr. Trump was elected in 2016. Republicans’ self-reported confidence remained well above Democrats’ for the entire Trump administration, until the election caused the pattern to reverse again.

“It reflects what we’ve seen in the survey data the whole time, which is that everyone is tying their own political beliefs to their views of the economy,” said Laura Wronski, a research scientist for SurveyMonkey. “It’s just kind of crazy to see how entrenched these beliefs are.”

Democrats’ views of the economy have also shifted after elections, but generally less than Republicans’, a pattern that was particularly stark this year. Ms. Wronski said enthusiasm among Democrats might have been tempered because they did not see the election as an unmitigated victory.

Janet Garrow, a survey respondent in Seattle, said that she thought Mr. Biden would do a better job with the economy than Mr. Trump, but that she didn’t expect a quick rebound from the pandemic-induced recession.

“I think the economic impact is devastating, and it’s going to take people decades to recover,” she said.

A retired judge, Ms. Garrow, 67, said her own finances are stable. But she said the economy wasn’t working for many Americans even before the pandemic.

“There was a lot of stagnation,” she said. “Sure, you might have had a job, but did your wage or your salary go up with what your cost of living really was?”

Ms. Garrow, a Democrat, said she supported many of Mr. Biden’s signature policy proposals, such as raising taxes on the wealthy and making public colleges free to students from middle-class families.

Perhaps more surprising, some of Mr. Biden’s proposals earn support from Republican voters. More than four in 10 Republicans support raising taxes on people earning more than $400,000 a year. Three-quarters of Republicans support a proposal to guarantee paid sick leave to workers during the coronavirus pandemic.

Liberal economists with links to Mr. Biden say the results show the popularity of his plans and the challenges of reaching out to supporters of Mr. Trump whose economic hopes were low before he won the 2016 election.

“We live in a country where, for all of our lives, we have seen economic inequality increase — across incomes, across wealth, across firms,” said Heather Boushey, an economist whom Mr. Biden said on Monday he would name to his Council of Economic Advisers. “A lot of communities have been left behind. People have become frustrated.”

“One of the things about Donald Trump is he acknowledged that reality,” she said. “It would be important for people on both sides of the aisle to continue to acknowledge that.”

William Spriggs, the chief economist for the A.F.L.-C.I.O. labor federation, said that the polling reflected the “partisan politics” now embedded in economic confidence surveys, and that it offered a message to Mr. Biden on the importance of pushing for policies like paid leave that have attracted Republican opposition in Washington.

“We absolutely need it, on a zillion levels,” Mr. Spriggs said. “I think this is going to be the challenge for the administration — because things like this, which Americans understand are common sense, doesn’t mean it’s politically feasible. The Republicans who are in office thumb their nose at these polls. The issue is, will the administration take them on?”

George R. Hood, a survey respondent in northern Kentucky, said he identified as a political moderate, not a liberal. But he said the country needed to invest more in public health, education and other priorities, and he said it made sense to raise taxes on corporations and the wealthy in order to pay for that spending.

“I just don’t see the socioeconomic situation improving unless we’re willing to spend a little more money,” he said.

About the survey: The data in this article came from an online survey of 3,477 adults conducted by the polling firm SurveyMonkey from Nov. 9 to Nov. 15. The company selected respondents at random from the nearly three million people who take surveys on its platform each day. Responses were weighted to match the demographic profile of the population of the United States. The survey has a modeled error estimate (similar to a margin of error in a standard telephone poll) of plus or minus 2.5 percentage points, so differences of less than that amount are statistically insignificant.