The question of how Donald Trump ever got elected president has stumped some of the nation’s deeper thinkers. Jennifer Mercieca has a compelling answer in “Demagogue for President: The Rhetorical Genius of Donald Trump.”

Spoiler alert: Trump is not, in fact, a genius. He’s a sophisticated con man who used the tools of rhetoric to pick the pockets of the American body politic. He double-talked his way to power. He buried his opponents with an avalanche of gibberish. He convinced more than 60 million Americans that the barnyard odor of his bombast was actually the pungent aroma of pure truth.

How did that happen? This book shows us by dissecting his demagogic language with a particularly precise scalpel. In doing so, it deserves a place alongside George Orwell’s “Politics and the English Language” and Harry G. Frankfurt’s “On Bulls---.” It’s a brilliant dissertation on Trump’s patented brand of balderdash. That makes it one of the most important political books of this perilous summer.

“Political language,” wrote Orwell, “is designed to make lies sound truthful and murder respectable, and to give an appearance of solidity to pure wind.” As Trump batters our country with his lies, which pummel us like the pellets of a ceaseless freak hailstorm, the falsehoods fly so fast and thick that we barely have a chance to examine them. How do they work? Why do they work?

Mercieca is an academic, yet her book is mercifully free of scholarly cant. It’s lively, clear, concise and remarkably good-humored, given its ill-tempered subject. She has done her homework and then some, poor soul: “I’ve watched and rewatched every Trump rally,” she writes. “I’ve read Trump’s books. I’ve watched all of his interviews and read his tweets. I’ve read as many articles as I could about what Trump was doing and why in traditional and nontraditional media. I’ve read white nationalists, conspiracy theorists, and the manosphere — all Trump’s people — which helped me make sense out of Trump’s more perplexing appeals.”

She explains Trump’s demagoguery — no easy matter — by analyzing it through the classic principles of rhetoric. This could be tedious in the wrong hands, but she makes it exhilarating, methodically revealing the insidious crowd-controlling methods of an autocrat.

Ad populum — appealing to the wisdom of the crowd — is Trump’s “many people are saying” strategy for framing his lies. He has tried to convince the nation “that the corrupt establishment used political correctness to hide its agenda, but that he, speaking for the wise crowd, saw through the corruption and the politically correct doublespeak,” Mercieca writes.

“Hey,” Trump told a rally in Birmingham, Ala., in November 2015, “I watched when the World Trade Center came tumbling down. And I watched in Jersey City, New Jersey, where thousands and thousands of people were cheering.” Trump never saw anything of the sort. When challenged, he first attacked the press, then doubled down before another crowd: “I received hundreds of phone calls over the couple of days since I said it from people saying, ‘Mr. Trump, you’re right. You’re right. We saw it. We live in New Jersey; we saw it.’ ”

Trump is a master of ad baculum — threats of force or intimidation. Debating Hillary Clinton, he brought out the big stick, as Mercieca reminds us: “If I win, I am going to instruct my attorney general to get a special prosecutor to look into your situation.” When Clinton responded that “it’s just awfully good that someone with the temperament of Donald Trump is not in charge of the law in our country,” he interrupted her to sneer, “Because you would be in jail!” Someday we will look back on the videos of Trump leading crowds in chants of “Lock her up!” and wonder how we fell so far.

Trump also used the trope of paralipsis to pave his path to power. That’s the forked-tongued-devil trick: “I’m not saying; I’m just saying.” It’s how Trump puts out falsehoods thinly veiled in implausible deniability: Oh, I was joking. I was being sarcastic. I never said it. On the day he secured the Republican nomination in May 2016, he called into “Fox and Friends” with a scalding libel of his vanquished opponent, Sen. Ted Cruz, linking his father to the JFK assassination: “You know, his father was with Lee Harvey Oswald,” Trump said. “Nobody talks about it. . . . What was he doing with Lee Harvey Oswald?”

A damnable lie, defended by drivel: “I’m not saying that he conspired; I’m just saying that it was all over the place. . . . I didn’t believe it, but I did say, ‘Let people read it’ ” — as they did in the National Enquirer. And then he blamed the whole thing on you-know-who: “The press takes that, and they say, ‘Donald Trump and his conspiracy theories; he went out and said his father was with Lee Harvey Oswald, and he assassinated the president.’ What did I do? I know nothing about his father. I know nothing about Lee Harvey Oswald.”

Mercieca defines Trump’s use of ad hominem personal attacks and his “America First” jingoism, along with the aforementioned rhetorical devices, as part of a larger tactic, in which he draws his audience into a black hole of conspiracy theories. You know it when you hear it from Trump: “believe me,” “this is so true,” “can you believe it?,” “what’s going on here?,” “there’s a lot going on,” “you never hear this” and the ever-popular “nobody even knows about it.”

“Because Trump was wise to the conspiracy, he positioned himself as a credible truth teller,” she writes. “Conspirators would never reveal their plot, which was why Trump was the one and only credible source of information. ‘You don’t read about this, right? They don’t tell you about this. They don’t want to tell you about this,’ Trump said knowingly.”

“Demagogue for President” has one flaw, though it’s part of its design: It’s about Trump’s campaign and not his time in the White House. The pursuit of power differs from its possession. And the one way in which Trump has grown in office is in the ferocity of his falsehoods.

But the book succeeds on its own terms, as a handbook for recognizing the real dangers of his dangerous nonsense. Mercieca concludes by calling Trump “a new kind of demagogue. He is a demagogue of the spectacle — part entertainer, part authoritarian.” He has used his rhetoric as a weapon to take advantage of the deep divisions in American democracy, conning the electorate into believing that he alone could heal them. He won by convincing just enough people that there are no facts and there is no truth.

This book can serve as a vaccine against a virus that threatens the survival of our democracy. Lord knows we need it.

Demagogue for President

The Rhetorical Genius of Donald Trump

By Jennifer Mercieca

Texas A& M. 338 pp. $28