This probably cost Ford the 1976 election — much as Mr. Romney’s opposition to “saving Detroit” may yet cost him this one, thanks to all the votes of auto-parts workers he stands to sacrifice in Ohio. Tragically, once-great cities like St. Louis or Newark never fully recovered from postwar deindustrialization. But urban living was far from dead. Instead, the American economy began to reinvent itself in cities, as they became cleaner, greener, safer, more prosperous, more fun. As the demographic wheel turned again, both new immigrants and a generation of Americans born and raised in the ’burbs moved back in.

Today, four-fifths of the population lives in an urban area — the highest percentage in our history. Although the country remains largely suburban, one in 12 Americans lives in a city of over a million people. More than ever, they are stakeholders, owning where previous generations rented, creating their own jobs and opportunities. Traditional liberal bastions like the Upper West Side of Manhattan are now filled with the owners of co-ops and condominiums worth hundreds of thousands, even millions of dollars. Over 140,000 New Yorkers in all — or nearly 4 percent of the labor force — work out of their homes. The percentages are even higher in Los Angeles and Chicago. Most of these individuals are skilled, highly educated “job creators” for themselves and others — the very demographic that Republicans claim to want to attract.

Some have managed it. The Upper West Side voted for the re-election of both the businessman Michael R. Bloomberg and the former prosecutor Rudolph W. Giuliani. Over the past 25 years, cities like Indianapolis, San Diego and even Los Angeles have elected — and re-elected — Republican mayors.

Yet the national Republican Party still can’t get seem to get past its animus toward the very idea of urban life. The only place that Amtrak turns a profit is the Northeast corridor — yet all Republicans can think to do is privatize it, along with the local rail lines on which millions of Americans have been commuting into cities to work for as long as a century and a half. Republicans promise to ban same-sex marriage, make it easier for anyone to get a gun, delegitimize and destroy what they mockingly call “public employees’ unions,” and deport the immigrant workers performing so many thankless but vital tasks.

In short, they promise to rip and tear at the immensely complex fabric of city life while sneering at the entire “urban vision of dense housing and government transit.” There is a terrible arrogance here that has ramifications well beyond the Republicans’ electoral prospects.

There wasn’t so much as a mention of cities in the debate on domestic issues the presidential candidates had last week. Nor did the Democrats have much to say about cities at their convention in Charlotte, N.C. They didn’t have to. Politically, Democrats don’t have to say anything about the urban experience; they embody it. But in too many cities this allows them to keep running corrupt and mediocre candidates.