Learn English – Is the phrase “step foot” a recent misuse of the phrase “set foot”

The British equivalent, though arising later than the American ten-foot pole, is “not touching s.o. or s.th. with a barge pole”:

The British get dog sick, leave footmarks and they wouldn’t touch some things with a barge pole. Americans get sick as a dog, leave footprints and wouldn’t touch some things with a ten-foot pole. — Catherine McCormick, British-American/American-British, 2001.

One of the earliest attestations for the British usage suggests a fairly recent coinage:

…he would not touch him with the end of a barge pole—(roars of laughter). — Oxford Times, 7 Oct. 1876. BNA [paywall]

The first instances include the end of the barge pole, which would be dropped on its way to a frozen expression. More telling, however, is that the metaphorical barge-pole could elicit roars of laughter, as if it were some novel witicism rather than a well-known cliche. Sir Randolph Churchill could still use it as a laugh line in 1884.

In America people had far more experience with a common measuring device than they did with barges, which after the emergence of the railroad receded in commercial and cultural importance.

The ten-foot pole in this expression is not a pole that happens to be ten feet long, but an open compound denoting a measuring tool just as yardstick is a closed one. With the wide availability of cheaply manufactured pocket metal tape measures in the 1920s, ten-foot poles were no longer useful or convenient — except in the metaphor which engendered the expression in the first place:

The early farmer had to build a cabin and barn or stable. Structures were built using a 10-foot pole, thus the old saying, “I wouldn’t touch it with a ten foot pole.” — George Wanamaker, “Measurement on the Farm,” June 2011, farmcollector.com

A ten-foot pole, along with a sixteen-foot surveyor’s pole, equipped an expedition in 1728 to survey the boundary between Virginia and North Carolina, which William Byrd (read all about his sex life in the Secret Diaries!) described in a book published a decade later:

At the same time, we found the Ground moist and trembling under our feet like a Quagmire, insomuch that it was an easy matter to run a Ten-Foot-Pole up to the Head in it, without exerting any uncommon Strength to do it. — William Byrd, Histories of the Dividing Line Betwixt Virginia and North Carolina, 1738 (repr. 1929), 62.

I have been unable to verify a mid-18th c. origin for the expression, but no 19th c. usage of ten-foot pole listed here would be a novelty — except, of course, the patent notice for one that conveniently folds up:

Having thus described my invention, I claim as new and desire to secure by Letters Patent as a new article of manufacture, a ten-foot pole made in four sections, the two middle ones hinged together and provided with slide E... — Specifications and Drawings of Patents Issued from the U.S. Patent Office for June 1875.

Clever farmers could easily make their own:

Among the things which are found convenient in every farmer's work-shop is a ten-foot pole, made thus: A piece of wood, one and a quarter inches square and ten feet long, is nicely smoothed with the plane, and then marked as follows ... —American Agriculturist 49 (1890), 259.

Ten-foot poles could be used in surveying, laying out a field or a large flower bed, measuring out a court for lawn tennis, testing the depth of flood water, for any number of tasks in the building trades:

He accordingly measures off eight feet from the end of one sill, and there makes a mark; he then measures off six feet on the sill lying at right angles with the first, and makes another mark; he then lays on his ten foot pole… — The Farmers' Cabinet, and American Herd-book, 1840.

and even a sign of celebration:

He stood upon the timber to be raised, swung his ten foot pole, and cried out, “Altogether, Altogether, ALTOGETHER, lift altogether;” and thus the massive front was erected, and there it stands to this day, as the result of united effort. — The Well-Spring, 3–4 (1846), 180.

Waving about a modern retracting metal tape measure — even in bright Stanley yellow — just wouldn’t have the same effect.

One of the first appearances of a ten-foot pole measuring a metaphoric distance in an American newspaper discusses a political matter of the day:

Last year, when running for the Legislature, the “whigs” would not touch [Henry] Clay with a ten foot pole ; but many now declare they will not vote for any one that is opposed to Clay. — The North Carolina Standard (Raleigh), 12 June 1839.

Now a bland narrative that basically says “It was a big yardstick” has far less currency than a macabre tale of dispatching decomposing corpses in New Orleans — all folk etymologies, no matter how outlandish, are always entertaining — but I’m afraid a measuring tool from the 18th and 19th centuries that was part of daily life for many is a far more likely, though dull, scenario.

Cortesy to commenters, the phrase "Till death do us part" is a more fancy way of saying "Until Death parts us". Since we surely cannot say "Until Death aparts us", the whole original statement is grammatically incorrect which is the direct answer to my question.