As Garry Trudeau sat on the stage of the National Portrait Gallery this month, the “Doonesbury” creator was asked how his three decades of satirizing Donald Trump have proved so prescient. Trudeau denied any powers of cartoon prognostication, chalking it up to a humorist’s trained response to the news of the day, including Trump’s earlier occasional feints at running for president. With a wry smile, the artist insisted he was doing little more than reading headlines and meeting deadlines.

Yet Trudeau, on a stop to promote his latest “Doonesbury”-on-Trump book, was playing it humble.

In those early days of the late ‘80s, Trudeau initially saw Trump as other New Yorkers did: a consistent glitzy presence in the gossip and business columns, almost a caricature of a real estate titan who wanted to shine brightest along the Manhattan skyline, like a beckoning light along a Gatsby dock. Yet when Trump began to criticize Washington in full-page newspaper ads, positing that he would make a better national leader than the Reagan/Bush-era Beltway losers, Trudeau began fitting Trump for an insightful bespoke debut in his Pulitzer Prize-winning comic strip.

Back then, the leaner, auburn-locked Trump was a satirical target almost entirely because of twin exercises in excess: his gilded acquisitions and the lengths he would go to bask in a limelight. This Trump, in Trudeau’s sardonic vision, was given to ordering up his own Sistine Chapel-style frescoes, only it was The Donald whose finger touched the hand of God. This Trump could seemingly buy everything except a sense of self-deprecation.

The other Trumpian trait that the cartoonist pegged and parodied right away was the salesman’s patter larded with superlatives. Even then, everything was the biggest and best, as Trudeau skewered the brands and beauty pageants and sex-life bravado of the “Doonesbury” Trump — a relatively harmless huckster who put the “hype” in “hyperbole.”

Today, though, Trudeau can no longer treat Trump like the occasional one-week sideshow. The cartoonist draws weekly instead of daily now, and more often than not, the Sunday “Doonesbury” pans for comedy gold amid the president’s 24/7 largesse. The resulting strips have proved popular, as collected in two recent books, including this fall’s “#SAD! Doonesbury in the Time of Trump.”

Shortly before the 2016 election, Trudeau published the bestseller “YUGE!,” which collected 30 years of “Doonesbury” strips featuring Trump. Looking back at the vintage work, it’s easy to see how quickly Trudeau grasped the essence of public Trump — the insatiable hunger for attention, the dizzying sense of entitlement, the playground petulance of one-upmanship, the embarrassing sense of decor and decorum and, always, the ravenous appetite for acquisition of objects and locations and people.

“#SAD!,” by contrast, is a more contemporary, mostly post-election take. We have fully moved into “Trump’s America,” in which the president tweets insults at all hours, the White House press office scrambles to explain his rogue rants and most any report that isn’t glowing might be decried as “fake news.”

Trudeau is often asked whether a figure as over-the-top as Trump is beyond lampooning — a question that also gets asked of such late-night comedic presences as Stephen Colbert and “Saturday Night Live” regular Alec Baldwin. But at his recent Smithsonian Associates talk at the portrait gallery, Trudeau noted that exaggeration is but one tool in the satirist’s belt.

That fact is deftly reflected in “#SAD!” The comic strip that would become “Doonesbury” was born 50 years ago this autumn in the Yale Daily News, and Trudeau has spent a half-century refining his angles of attack. So although Trudeau’s Trump relies on exaggeration for physical caricature — the “Doonesbury” president is a heavily jowled and hunched-over figure with patchwork sprigs of hair — the writing of the recent strips aims closer to reportage in tone, with the jokes often sprouting out of blatant, blunt-force contradictions of fact and logic that closely mirror reality.

That parodic approach works best when you can nearly hear Trump giving voice to this verbiage in a real-world setting. In a strip from late 2016, for instance, a month after the election, “Doonesbury’s” Trump is decrying “nasty stories,” “lying, disgusting reporters” and the “slime” that is the mainstream media. The strip’s language hews so closely to the truth of a Trump salvo that it verges on winking dictation.

Trudeau finds humor, too, in skewering those who seem to embrace the president uncritically. His best foil in this service is the strip’s conservative correspondent, Roland B. Hedley Jr., who deploys a true believer’s ability to deny journalism thanks to an “a la carte” comprehension of the facts and a shameless habit of tweeting his half-baked retorts.

Trudeau won his editorial cartooning Pulitzer in 1975 largely for his depiction of President Richard Nixon as a paranoid Shakespearean figure who tried hiding behind the escalation of his stonewalling tactics. Since then, the left-wing cartoonist has consistently been hardest on Republican presidents — yet even Trudeau puts Trump in a league of his own.

The cartoonist renders the 45th president as unleashed id free of guilt, empathy or deep self-examination. “Doonesbury’s” satiric Trump has so many blind spots, it’s as if he’s encircled by steel slats.

The cartoonist also smiles at the kind of president who suggests that the legality of SNL satire should perhaps be challenged in the courtroom. Parody and satire have had their day in the Supreme Court and won, Trudeau notes, in the famed 1988 Hustler Magazine v. Falwell case that specifically cited “Doonesbury.”

So when “Doonesbury’s” Trump jokes about “loosening the libel laws,” as he does in a 2016 strip, Trudeau obviously delights in prodding and poking the president precisely where he seems most sensitive.

Trump once praised “Doonesbury,” early on. Since then, he has called the strip “a lesson in pure salesmanship” — an intended swipe, yet a trait that the president typically admires. Between Trump and Trudeau, clearly only one is suffering from an irony deficiency.