Johnson, who is looking to become only the second player after Tiger Woods to win the title as world No 1, carded a second round of 67 to set a daunting clubhouse target of four under par.
That did not look like being challenged until the wind surprisingly died in late afternoon and Poulter was among those to take advantage, three birdies in four holes from the fourth taking him to within a shot of the lead.
However, the 42-year-old then thinned a bunker shot on the eighth across the green, duffed his next shot into heavy rough and ran up a triple-bogey seven, with a bogey on the ninth completing a miserable half an hour.
The resulting 72 left Poulter on one over par alongside fellow Englishmen, Justin Rose and Tommy Fleetwood, Henrik Stenson and defending champion Brooks Koepka, with Scott Piercy and Charley Hoffman the nearest challengers to Johnson on level par.
The cut fell at eight over par and saw Jordan Spieth, Rory McIlroy and Woods all make early exits, Spieth missing out by a single shot after following four straight birdies with bogeys on the 17th and 18th.
McIlroy’s 70 was a 10-shot improvement on his opening round but still meant a third straight missed cut in an event he won in record-breaking fashion in 2011, while Woods also finished 10 over par following a 72.
Poulter was left to try to take the positives from his position on the leaderboard, but admitted: “The best outcome for me is to get it out of my mind.
“I felt stupid knifing the first shot [out of the bunker], I felt more stupid semi-chunking the next one and I didn’t do that well with the next one either. But if you had offered me one over and tied fourth at the start of the week I would have taken it.”
Rose expressed similar sentiments after ending his 70 with back-to-back bogeys, adding: “I found it hard to concentrate coming in, there were a lot of distractions, but I’m in a good spot and happy.”
Johnson was no doubt even happier after seeing his four-shot lead restored by the late drama as he tries to become the first player to win the US Open the week after a victory on the PGA Tour.
“I like golf courses where par is a really good score and here, on every hole, par is a good score,” said Johnson, who regained top spot in the world rankings following his six-shot win in Memphis. “I played well and my speed on my putts has been very good. To hole that one on the seventh (from 45 feet) was a nice bonus.”
Fleetwood finished fourth at Erin Hills last year and is relishing another tough challenge over the weekend as he looks to become only the third English winner of the US Open since 1924.
“I have a lot of patience and the tougher the conditions the more I feel I can grind it out and will my way around,” the European No 1 said. “If you are going to win the US Open, which is one of the biggest tournaments in the world, it should be that kind of test.
“It’s a tournament that sets up for good ball strikers, which is one of my strengths. Yesterday we got beat up and today turned into survival midway through the wind when it was cold and raining, but I managed to get something going with some birdies at the end.”