When pundits claim Donald Trump can win the presidency, they often evoke a fabled political species: “Reagan Democrats.” “Are Reagan Democrats becoming Trump Democrats?” wondered CNN commentator Jeffrey Lord last fall in The American Spectator. “I think there’s a lot of Reagan Democrats waiting to vote for him,” declared MSNBC’s Chris Matthews in January.

This almost certainly isn’t true. The more you examine it, the more far-fetched the claim that Trump can win the presidency by luring vast numbers of “Reagan Democrats” looks.

What is a “Reagan Democrat?” At its most literal, it’s a Northern, white, noncollege-educated Democrat who actually voted for Ronald Reagan. But there aren’t many of them left. The median member of the voting-age population in 1980 was 40—and, according to the CDC, the average white male who was 40 in 1980 lived another 34 years. So the typical blue-collar white man who voted for Reagan in 1980 can’t vote for Trump this fall. He’s dead.* White men born in 1950 die on average at age 66. That’s this year. White working-class men die even earlier. The average white woman who at age 30 voted for Reagan in 1980 will live a bit longer: until 2022. Most white working-class women, however, won’t make it until then.

So when people talk about “Reagan Democrats” today, they don’t mean Democrats who actually voted for Reagan. They mean the people who resemble them demographically: Northern blue-collar whites. But blue-collar whites don’t enjoy the same political significance they did in the 1980s. In the 1988 presidential election, they constituted more than half the voters. This fall, they’ll constitute roughly one-third. A new Center for American Progress report, brought to my attention by The Washington Post’s Greg Sargent, notes that in the classic “Reagan Democrat” states of Pennsylvania, Ohio, Michigan, and Wisconsin, blue-collar-whites’ share of the electorate will shrink two percentage points between 2012 and 2016 alone.

Not only are blue-collar whites a smaller share of the electorate than in 1980, they also behave differently. As American University political scientist David Lublin notes, “The early 1980s were the height of weak partisanship with voters much more willing to defect from their party in elections than today.” Back then, Democrats were less homogenously liberal. Lots of whites with fairly conservative views on race, gender, and national security still identified with the party. So ideologically, voting for Reagan wasn’t much of a stretch.

Since then, however, American politics has witnessed a massive ideological “sorting.” The kind of conservative blue-collar whites who would once have been “Reagan Democrats” are now mostly Republicans. As The Washington Post’s Phillip Bump notes, working-class whites are almost 10 percentage points more likely to identify with the GOP than they were in 1980. Those blue-collar whites who remain Democrats are more liberal. It may be because they’re members of unions and thus more sympathetic to a pro-government message. It may be because they’re Millennials, who even in the white working class tend to be more secular, more pro-gay marriage, and less racially resentful than their parents and grandparents. It may because they are women, who are somewhat more liberal than men overall.

The point is that, because of this “sorting,” notes Emory’s Alan Abramowitz, “Party ID [now] predicts vote choice very well.” In 2012, Mitt Romney won Republicans 93 to 6 percent. Obama won Democrats 92 to 7 percent. Not many people cross party lines in presidential elections anymore.

To mobilize large numbers of “Trump Democrats,” Trump would have to change all this. But there’s little evidence that he can. A March Washington Post poll found that in a hypothetical matchup with Trump, Hillary Clinton wins Democrats 86 to 9 percent. That means, right now, that Trump does indeed gain a few more Democratic defections than Romney did. The problem is that Trump is only winning Republicans 75 to 14 percent. In other words, more Republicans are planning to vote for Hillary than Democrats are planning to vote for Trump, which helps explain why Clinton is leading in almost all the head-to-head polls.

Perhaps Trump voters are embarrassed to admit that they support him, and polls thus far understate his support. But Lublin points out that, so far in the primaries, this hasn’t been the case. Trump hasn’t done better on election days than the polls predict. He has done slightly worse. Nor has 2016 witnessed an avalanche of white blue-collar Democrats crossing over to vote for Trump in Republican primaries. GOP primary turnout has been higher: higher than it was in 2012 and higher than the turnout on the Democratic side. And Trump does seem to be mobilizing a significant number of first-time voters. But not many of these are Democrats. According to exit polls, while some states have seen more Democrats crossing over to vote in Republican primaries than in 2012, many others have seen fewer. In Michigan, for instance, a key “Reagan Democrat” state, the number of Democrats who voted in the Republican primary is way down.

The electoral fantasy that Trump can win the presidency by luring vast numbers of blue-collar whites who wouldn’t otherwise vote Republican is akin to the ideological fantasy that he can keep America prosperous and safe by banning Muslim immigration and getting Mexico to pay for a wall on the U.S. southern border. It’s a fantasy that he can roll back history to a time when whites enjoyed more control, both over nonwhites inside the United States and over those who wish to enter from outside. This throwback fantasy is appealing inside a Republican Party where white voters remain unquestionably dominant. But in the America of today, reality is very different. And, unfortunately for Donald Trump, it’s in today’s America—not Ronald Reagan’s—that he must compete this fall.

* This article originally miscalculated the life expectancy of a white, male Reagan supporter in 1980. We regret the error.