Today's Democratic Party is not your father's Democratic Party

There’s a popular portrait of a “Trump voter.” He’s a white man without a college degree, and so loyal that he would stick by Mr. Trump no matter what.

There’s a reason the stereotype exists: Mr. Trump’s strength among white working-class voters, particularly men, put him over the top in the decisive battleground states in 2016. And his approval ratings have been extremely steady, despite a year of controversial tweets and policy decisions. But it’s not the whole story.

Yes, white voters without a college degree shifted decisively from Barack Obama to Donald J. Trump in 2016. But these voters actually made up only a slightly larger share of Mr. Trump’s coalition than they did of the previous three Republican nominees’ coalitions.

And while Mr. Trump has a large and resilient base of supporters, a sizable share had reservations when they cast their ballots for him and continue to have reservations about him today. A small but meaningful number of his voters, particularly women, appear to have soured on him since the election.

Understanding the breadth of Mr. Trump’s coalition is important to understanding the Republican Party’s position heading into the 2018 midterms. Mr. Trump’s most enthusiastic supporters were vital to his victory in the primary, and Obama-Trump voters in old industrial towns were decisive in the general election. But the midterms could be decided by voters at the edge of Mr. Trump’s coalition and of the public's imagination: stereotype-defying female, college-educated or nonwhite Trump supporters, who are somewhat likelier to harbor reservations about the president. They may have been reluctant to back him, but they were still essential to his 2016 victory and are essential to the G.O.P.’s chances today.

This more nuanced picture emerges from a survey of validated voters on Pew’s American Trends Panel, a representative sample of American adults who agreed to take Pew surveys every month. The panel allows a rare, direct measurement of how voters have shifted over time.

Pew asked panelists how they voted in November 2016, and the responses were matched to voter records that indicate whether a panelist actually cast a ballot. It’s a big advantage over typical polls, which struggle to distinguish shifts in public opinion from the effect of a new set of respondents in each poll. It offers perhaps the clearest picture yet of who supported Mr. Trump and how his voters feel about him today.

Trump’s voters are demographically similar to Mitt Romney’s

If you want to understand why Mr. Trump won the presidency, there’s one big reason: white voters without a college degree. They put Mr. Trump over the top in disproportionately white working-class battleground states where Mr. Obama fared relatively well, like Pennsylvania, Wisconsin and Michigan.

But Mr. Trump’s supporters aren’t monolithic. Nor is his coalition necessarily dominated by the groups that broke most strongly for him.

Just 33 percent of Mr. Trump’s supporters were white men without a college degree. A majority of Mr. Trump’s supporters defy the stereotype: They were either women, nonwhite or college graduates (or some combination of those).

Over all, 47 percent of Mr. Trump’s voters were women. And though he struggled among affluent college-educated whites for a Republican, he still won 44 percent of voters making more than $150,000 per year, according to the Pew data, and nearly 40 percent of college-educated white voters.

Perhaps surprisingly, Mr. Trump’s voters were about as likely as the supporters of other recent Republican nominees to hold a college degree.

How did the number of white working-class Republican voters stay so constant? Republicans have been winning a progressively larger share of white voters without a degree, but the group is shrinking over all. The result is that the two trends have basically canceled each other out.

White, non-college voters did break strongly for Mr. Trump but those voters make up an ever-decreasing share of the electorate.

At the same time, Republicans have lost ground among college-educated and nonwhite voters, but those groups have been growing as a share of the electorate. So oddly, a room full of Trump voters would be similar to a room full of George W. Bush voters, at least based on their race and education.

A room full of Democrats, on the other hand, would look a lot different. The party is doing increasingly well among growing portions of the electorate, and worse among the shrinking number of white working-class voters. Over all for Democrats, white voters without a degree have fallen from 43 percent of John Kerry’s voters to 26 percent of Hillary Clinton’s.

The shift among college-educated white voters was particularly sharp, and the Pew data is one of the strongest pieces of evidence indicating that Mrs. Clinton did far better among this group than initially believed. In the Pew data, she carried college-educated white voters by 17 percentage points, a huge shift from 2012, when Mitt Romney won that group.

It’s a very different story from the exit polls, which showed Mr. Trump winning college-educated white voters. There’s little doubt that the exit polls were wrong. Virtually all other survey data, along with the precinct-level election results, suggest that Mrs. Clinton won college-educated white voters and probably by a big margin.

The Trump voters most likely to stop supporting him: Women and the college-educated

There has been little change in President Trump’s approval rating in the last 18 months, and so it’s often assumed that nothing can erode his base of support. The Pew data suggests it’s not so simple.

Yes, nearly half of Mr. Trump’s voters have exceptionally warm views toward him: 45 percent rated their feeling toward him as a 90 or higher out of 100, a figure that is virtually unchanged since his election. But a meaningful number of his voters had reservations about him in November 2016, and even more Trump voters held a neutral or negative view of him in March.

Over all, 18 percent of Mr. Trump’s voters gave him a rating of 50 or less, on a scale of 0 (coldest) to 100 (warmest), up from 13 percent in November 2016.

It is worth noting that the November 2016 Pew survey was taken after Mr. Trump won the presidency, at the height of his post-election honeymoon. But even when you consider the slightly lower ratings voters gave him in the months before the election, the big picture is the same: A modest number of Mr. Trump’s voters didn’t like him that much then, and don’t like him much now.

Women, and especially college-educated women, are the likeliest Trump voters to have serious reservations about him in 2018: A striking 14 percent of the college-educated women who voted for him hold a very cold impression of him, up from just 1 percent in November 2016.