It's true: America of the 1870s, or a particular Hollywood fantasy thereof, is having its fashion moment.
Not only do the youthful boutiques stock heavy denim, thick wool trousers, plaid flannel jackets, leather suspenders, waistcoats, workboots, kerchiefs and collarless shirts, their patrons are topping their clothes with Klondike prospector beards, handlebar mustaches and mutton-chop sideburns. They are wearing their shirts buttoned up to the neck, and I have even seen a couple of very pretentious guys with sleeve garters – those expandable metal bracelets you put on your bicep to keep your shirt cuff at exactly the right length. (Those haven't been fashionable since about 1925.)
Some downtown streets are starting to look like sets for an early Clint Eastwood movie – soon they'll be putting wooden rails for tying horses outside every microbrewery.
As soon as they start wearing top hats with their outfits, they will have crossed the line into full-on pastiche, but so far, the adherents of the movement don't want to be too obvious about the fact that they are dressing in historical costume, the way the "swing revival" kids of the 1990s were. (Remember them, with their two-tone shoes and their porkpie hats?)
Periods of nostalgia are impossible to predict or explain. Big movies and TV shows such as Mad Men can sway things, but they can't be seen solely as causes: They, too, are part of the zeitgeist, the moment's general longing for another moment. Mad Men is an effect of sixties nostalgia as much as a cause.
It's interesting that the mid-19th-century fashions being aped now are never those of the privileged. They're not frock coats and brocaded waistcoats – they are boots and dungarees. It's the image of the hard man, the grizzled man, that's popular. Perhaps this is to disguise that the look's most dedicated followers actually spend their days in front of computer screens, not working on railways.
Here's a tip for the best way to rock the look: Don't overdo it. A waistcoat and a kerchief is fine; add a clay pipe and suspenders and you might as well pack a toy six-shooter. You'll look like a boy playing cowboy.