For the first time in decades, the wealthy are set to deliver a landslide victory for a Democratic presidential candidate.
While polling data on the rich is imprecise given their small population, polls of the top-earning households favor Hillary Clinton over Donald J. Trump two to one. The July Affluent Barometer survey by Ipsos found that among voters earning more than $100,000 a year — roughly the top 25 percent of households — 45 percent said they planned to vote for Mrs. Clinton, while 28 percent planned to vote for Mr. Trump. The rest were undecided or planned to vote for another candidate.
The spread was even wider among the highest earners. For those earning $250,000 or more — roughly the top 5 percent of households — 53 percent planned to vote for Mrs. Clinton while 25 percent favored Mr. Trump. The survey's margin of error was plus or minus four points.
It is unclear whether those patterns have changed since July. But if the numbers hold, historians and wealth experts say that next month's elections may prove to be the largest vote by the wealthy for a Democratic candidate in recent history.
''This would be a big deal, and fundamentally different from what we've seen before,'' said Andrew Gelman, professor of statistics and political science at Columbia University and co-author of the book ''Red State, Blue State, Rich State, Poor State: Why Americans Vote the Way They Do.''
The big question is whether Mrs. Clinton's potential sweep of the elite represents a structural shift in the politics and policy preferences of the wealthy, or simply a personal aversion to Mr. Trump. Either way, the vote would break decades of Republican dominance of affluent voters in presidential elections. It would also shed light on a growing debate about whether the wealthy are tacking to the left politically as more fortunes are created and concentrated in states like California and New York and throughout the left-leaning tech industry.
''Trump could be an aberration,'' Mr. Gelman said. ''Or this could be part of a political realignment. We probably won't know for years.''
Ipsos says its data suggests that the affluent are more anti-Trump than pro-Clinton. In the spring, Democratic-leaning voters making more than $100,000 were split evenly between Mrs. Clinton and Bernie Sanders. Republican-leaning affluent voters were split evenly among Mr. Trump, Ted Cruz and Marco Rubio. By the end of the summer, Mrs. Clinton had picked up nearly all of the Sanders-leaning affluent voters, while Mr. Trump failed to win as many of the Cruz and Rubio voters.
''The affluent vote seems to be more about the concerns over Donald Trump than the enthusiasm for Clinton,'' said Stephen Kraus, chief insights officer and director of the Ipsos Affluent Survey.
Since the 1950s, with few exceptions, upper-income voters have leaned more Republican than the broader population. In a study of national elections, Mr. Gelman found that ''census and opinion poll data since 1952 reveal that higher-income voters continue to support the Republicans in presidential elections.''
Mr. Gelman said the wealthy naturally favored policies that favor them, and Republican staples like lower taxes and smaller government were preferable than larger government and redistribution of wealth. ''They support policies that benefit their group, because in their view, those are the best policies and best ideas,'' he said.
If the wealthy voted according to their pocketbooks, their choice for president would be clear.
Mr. Trump has pledged to cut the federal income taxes of the top 1 percent by more than 25 percent, allowing them to keep an extra $215,000 each year, according to the Tax Policy Center. He would eliminate the estate tax, reduce regulations, cut the capital-gains tax rate and create a special, superlow tax rate for some business owners.
Mrs. Clinton, by contrast, would make the top 1 percent pay an average of $117,000 more a year while superearners in the top 0.1 percent would see their taxes go up more than $800,000 a year. She would also increase taxes on certain capital gains, limit loopholes used by the wealthy and target dynastic wealth with a steeper estate tax.
In recent decades, there is evidence that wealthier voters have been leaning more Republican. In 1956 and 1960, the share of Republican-identified voters in the top income quintile ''was only slightly higher in the highest than in the lowest quintile,'' Mr. Gelman said. By 2000, those at the top were more than twice as likely to identify as Republican than those at the bottom, according to Mr. Gelman's study.
The closest comparison to the current election among affluent voters is the one in 2008, when Barack Obama carried about half of voters who earned more than $100,000. Yet Mr. Gelman said John McCain still did better among the rich than the poor, and compared with the broader electorate, the wealthy voted Republican more often.
In the current election, Mrs. Clinton is poised to capture a far larger share of the affluent vote than Mr. Obama. And if the numbers hold, the elite would lean more Democratic than Republican for the first time in at least 50 years, Mr. Gelman said.
Among the rich and superrich, the politics are more divided. In the run-up to the 2012 election, 61 percent of millionaire voters (those with investable assets of $1 million or more) supported the Republican nominee, Mitt Romney, according to a survey from the Spectrem Group. In the 2008 election, while more than three-quarters of millionaire families favored Mr. McCain, two-thirds of families worth $30 million or more supported Mr. Obama.
Some argue that the rich have become more Democratic because many of the richest states, like California, New York, Connecticut and Maryland are blue. Yet Mr. Gelman's research shows that while rich states lean more Democratic, affluent voters still lean more Republican.
''The Republicans have the support of the richer voters within any given state but have more overall support in the poorer states,'' Mr. Gelman said. ''Thus, the identification of rich states with rich voters, or more generally, the personification of so-called red and blue states, is misleading.''
In the current election, of course, neither candidate is publicly courting the wealth vote. Even Mr. Trump has been labeled a populist. Yet affluent voters are 15 to 20 percent more likely to vote than the broader population, according to Ipsos. Their financial support gives the wealthy an outsize voice in campaigns.
''I don't think either candidate wants to be seen as having the support of the 1 percent right now,'' Mr. Kraus said, ''even though they are both part of the 1 percent.''