A popular argument in recent years suggests that changing demographics yield good news for Democrats in upcoming elections. Josh Gelernter challenges that argument at National Review Online.

Democrats, and journalists, talk a great deal about how demographic changes are inexorably shifting the American electorate to the left. But they’re wrong.

The Democrats have founded their political fortunes on special-interest groups for more than 150 years — since at least the late 1850s, when Tammany Hall (the Democrats’ New York City political machine) was taken over by Boss Tweed, who began to use its political influence to support (and pander to) Irish immigrants (in particular), in exchange for votes. The Irish were the largest immigrant group in the country, and an increasingly powerful voting block. Thanks to Tweed and company, they became a voting block that invariably voted Democratic. The Irish continued to constitute the largest or second-largest immigrant group each year until the end of the 19th century, and you would have been forgiven for predicting that they would help deliver a permanent electoral advantage for the Democrats.

Starting with the 20th century, Irish immigration was eclipsed by Italian. Italian immigrants quickly began receiving Democratic patronage, and became a new core of the Democratic electorate. Italians continued to be the largest or second-largest immigrant group each year until the Second World War. Throughout that period, you could rely on Italians to vote overwhelmingly Democratic.

But then, in the 1960s, Italian-Americans started splitting their votes evenly between Republicans and Democrats. These days, the Irish-American vote is a reliable 50-50 split too. Why? Because the Irish and the Italians stopped being special-interest groups. After their initial isolation, the Italians and the Irish stopped being easily divisible from the average American. They didn’t want custom-tailored treatment, they just wanted the same shot at the American dream that everyone else had. They’d been assimilated. They stopped being primarily Irish or Italian and became, first and foremost, American. And that meant that Democratic pandering didn’t work anymore. There was no more distinct group to pander to.