Jones wrote in an email that, according to the new General Society Survey data, “today, the religiously unaffiliated outnumber white evangelical Protestants” by nearly 7 percentage points.

The decrease in the percentage of white evangelicals began, Jones continued, during President Barack Obama’s eight years in power. According to Jones,

the anxieties that produced about a changing country and white evangelicals’ place in it were actually integral to pushing white evangelical Protestants toward support for Donald Trump in 2016. So these changes are not just now upon us; they’ve been an engine driving the political dynamics for some time. But the new G.S.S. data shows them continuing unabated.

In other words, in the short term, as they feel they are being eclipsed, white evangelicals become more politically engaged, more assertive — and more dangerous to their opponents.

Burge claims, however, that the long-term future of the conservative evangelical movement could be in doubt:

It’s going to run into a demographic brick wall going forward. 81 percent of evangelicals in 2018 were white, compared to 72.4 percent of the overall population.

Among younger voters 18 to 25, “only 60 percent are white,” according to Burge.

Ultimately, Burge argued,

hitching their wagon to Trump may stave off some losses now, but it may be a fatal strategy in ten or twenty years.

While the trends highlighted in the Cooperative Congressional Election Study and General Social Survey are generally favorable to the Democratic Party, they also point to obstacles Democrats face.

Stephen Ansolabehere, a political scientist at Harvard, noted that more than two thirds of sitting presidents have been re-elected. He went on to point out that “presidential second term elections are driven strongly by the economy.” Ansolabehere maintains that

if the economy is steaming along Trump will have the wind in his sails. The presidents who faltered in recent memory are Carter and Bush senior, both of whom faced weak economies.

Brian Schaffner, a political scientist at Tufts, raised another issue. “There is certainly some good news for Democrats,” he wrote, but “the caveat seems to be that opinion is mostly moving for the people who were already inclined to support Democrats,” before adding: “What we don’t see is much movement among Republicans.”

Schaffner, who serves along with Ansolabehere as a principal investigator at the Cooperative Congressional Election Study, also cautioned in an email against putting too much stock in the data showing that some voters who had cast ballots for Trump switched to Democratic House candidates in 2018.

“The C.C.E.S. data do show that about twice as many Trump voters flipped to supporting Democrats in 2018 as Clinton voters switched to Republicans,” Schaffner wrote, “which suggests that a lot of those ‘blue wall’ states from 2016 may be leaning against Trump slightly as we head to 2020.”

He warned, however, “that all of these shifts are relatively small in the aggregate, which means we aren’t necessarily too far from where we were in November, 2016.” While Trump in 2016 benefited from “a decent amount of luck” in losing the popular vote but winning the Electoral College, “it is certainly possible that it could happen again absent some larger shift in opinion.”