John Daniel Davidson of the Federalist pokes holes in a left-wing argument against conservatives.

The [New York] Times is of course referring to so-called “replacement theory,” the idea that global elites are trying to “replace” white Americans with immigrants and foreigners, which the Times thinks is a common belief among Republicans. Not to be outdone by the Times, the Washington Post’s editors on Monday declared, “what was once on the fringes has now been given currency, thanks to the Republican Party’s tolerance of white nationalists who count themselves as part of its base.”

The notion that “replacement theory” is mainstream on the right, much less in the GOP, is of course abject nonsense. But the accusation serves a purpose. By conflating the conspiracy theories of maniacs like the Buffalo shooter with legitimate calls for, say, border security and controls on illegal immigration, the left can smear all Republicans as white supremacists.

Doing so serves a useful purpose for Democrats. If Republicans are the party of people who believe global elites are trying to “replace” white Americans with immigrants and foreigners, then any calls to fix our immigration system or solve the ongoing crisis at the border must be in bad faith, nothing more than rank racism thinly disguised as a respectable-sounding immigration agenda.

It also serves Democrats in another way: it helps mask an electoral agenda they once openly espoused. It’s no secret that Democrats think mass illegal immigration will accrue to their electoral advantage over the long term. For years, they have felt comfortable saying so routinely on national television.

Indeed, the notion that “demographics is destiny” has been a long-running belief among Democrats, famously spelled out in John Judis and Ruy Teixeira’s widely acclaimed 2004 book, “The Emerging Democratic Majority.” Part of their argument rests on the assumption that immigration, legal and illegal, will swell the ranks of Democrat voters and hasten the inevitable emergence of a permanent Democratic majority.

That theory, whatever its merits in 2004 or 2013, is looking weaker by the year.