SHANNON WHEELER has spent much of this year poring over thousands of President Trump’s tweets, and just when he believes he’s lost the ability to be shocked, @realDonaldTrump hits a fresh nerve.

“I keep thinking I’ve been inoculated,” says Wheeler, an Oregon-based cartoonist, “but then I read something new that [hits] like an adrenaline shot to the hypothalamus.”

The fruits of Wheeler’s creative endurance will go on display Tuesday, when the publisher Top Shelf releases his book “Sh*t My President Says: The Illustrated Tweets of Donald J. Trump.”

“I’m doing the same thing I did in high school,” the Eisner-winning cartoonist (“Too Much Coffee Man”) tells The Post’s Comic Riffs. “I would listen to my teachers and do drawings making fun of them.” Only now, he notes, he’s skewering the tweets of a man whose rhetoric stirs and influences and inspires and repulses millions.

And what Wheeler sees in the tweeting commander-in-chief is a leader who is often playing to his base, using his 140-character missives as trial balloons. “He thinks: ‘How is my audience going to respond to this?’ ” the cartoonist says. “Tweeting is like a thermometer for him.”

Or, as Wheeler writes in his book’s introduction: “His implicit message isn’t about himself, it’s about his reader. He encourages his fans to be themselves — not with aspiration, but indulgence. Be sexist. Be racist. Be fearful. Be selfish. Hate and fear the world.”

An initial challenge for Wheeler was how to sift through more than 30,000 of the verified account’s tweets (since 2009) for deeper meaning. He culled that total to about 1,000 of Trump’s least promotional tweets. From those, he found satiric clay to work with by identifying the president’s most repeated themes and compulsive narratives — from crowd size to ratings to identifying people he perceives as enemies. Beyond caricature and parody, he writes, “I want to show how he contradicts himself, and lead[s] the reader to question reality.”

“Every day, I wake up and look at my phone and wonder: ‘What happened last night [on Trump’s Twitter feed]?’ ” Wheeler tells The Post. “As horrifying as it is for people, it’s also a sort of entertainment for [much of] the country.”

In assessing the tweets honestly, however, Wheeler also aims to understand Trump voters. His conclusion: Much of that backing is not necessarily “a love of Trump,” he says, “but a hatred of the Washington situation, and it’s an anger that’s being acted out.”

As Wheeler’s approach to dissecting Trump’s prose evolved, so did his Trump cartoon character who appears throughout the book.

“He’s a bully,” Wheeler says of his caricature. “He’s like the fifth-grader who got held back one grade and he’s now a little bit bigger than you are and he’s still a kid, but you’re a little bit scared of him.”

Wheeler’s Trump is a rotund scamp with a mischievously fiendish spirit.

“I was trying to draw him ‘ugly’ and it was not working, and then I was starting to feel: ‘What is inside of him?’ It is the impish child. You think: ‘This is the [playground] kid who would be made fun of if he weren’t making fun of other people.”

“When I started drawing him as a monster — like an ogre, a mean person — another insight I had from his tweets is that he thinks of himself as a protagonist,” Wheeler says. “Once I realized that and started drawing him that way, it clicked into focus.”

Not all of Wheeler’s colleagues were pleased with that depiction, though. “Three political cartoonists implored me to draw him villainous,” the author says. “I was like: ‘It doesn’t feel right for me to draw him in that way. It doesn’t give me any insight to [visually] vilify him in that way.”

With that approach, instead of slinging mud that can turn matters opaque, he’s actually attempting to render a window into Trump. One example is how he focuses on his favorite Trump tweet.

“It’s his ‘I’m still doing my taxes’ tweet ,” Wheeler says. “I just drew a closed door, because that’s where Trump draws this kind of privacy. He will publicly expose himself about his proclivities and on all these other levels, but on money, he holds that very private.”

Perhaps Wheeler’s last true challenge with this book was turning in the final work in June, with a fresh Trump news cycle heating up. “As soon as we closed the book, there was a new slew of Russia stuff — it broke my heart,” the cartoonist says. “It was so juicy and funny.”

And even after half a year of poring over Trump’s own special brand of Twitterature, Wheeler is still stumped by one thing: “In all my work, I’ve never been able to figure out: How did we wind up with this president?”

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