Though the Briton played better golf in the second round at the daunting Olympic Club, he had left himself too much ground to make up after battling to an opening 79 on Thursday.
Donald mixed five bogeys with three birdies for a two-over-par 72 but his 11-over total of 151 was almost certain to be well outside the cut in the year's second Major.
"A little better today, but little consolation," the 34-year-old Englishman said after pressing too hard over his closing holes in dazzling sunshine at Olympic in a bid to accumulate further birdies. "It's not going to be good enough to play the weekend and obviously my troubles started yesterday.
"I was a little off, and that's not going to get you around a US Open course. I missed nine putts inside 10 feet yesterday and I just couldn't get the feel for the greens, the reads, the speed."
Donald, who became the first player to lead the money lists on both the European and US PGA tours last year, totalled 36 putts in the opening round on the small, fast-running greens at Olympic.
"If I had putted a little bit better yesterday I could have ground out a score today and maybe been somewhere decently placed for the weekend," the seven-times European Tour winner said. "But it wasn't to be and I'm trying to learn from it and come back stronger next time."
Donald, who has won tournaments on both sides of the Atlantic Ocean this year, said he had targeted an eight-over total after the second round to ensure he made the cut.
"So maybe shoot one under today," he added. "Something in the sixties, I think, might have been good enough. But I was pressing to try and make birdie ... that's a tough thing about a US Open, it's hard to be aggressive."
Asked whether he had suffered from self-imposed pressure to end his Major title drought, Donald replied: "That's the one part of my golfing resume in the last few years especially that I need to continually address and continually improve.
"I want to win one more than any of you guys know, and obviously I'll continue to try and do that. It was more a case of just not quite feeling too comfortable with the swing this week. And that happens.
"Unfortunately at Major weeks that's going to be magnified even more."
Donald, who has finished in the top five at the Masters, the Open and the US PGA Championship, plans to take the next three weeks off before returning to competition at next month's Scottish Open.
"Put the clubs away for a week probably, or two days at least, just to take stock of what I need to do and then back to the grind," he said.
The European Tour's Scottish Open is one week before the July 19-22 Open at Lytham St Annes in England.