AT THE outset of his acceptance speech Tuesday evening, 2016 Herblock Prize winner Mark Fiore made a vow to the Washington audience: Although a political cartoonist, he’d go his entire talk without uttering the word Trump.

“I won’t mention a certain orange-hued [candidate]. I’ll leave that to another Mark,” said Fiore, nodding to the front row and the speaker who would follow him: 2016 Herblock Lecturer and political analyst Mark Shields.

Many in the Library of Congress audience laughed, and some cheered. Too soon, it turned out. Even here, campaign-season promises are made to be broken.

About midway through his talk, Fiore reached for the name of a modern politician to plug in to a laugh line and said, “Trump” — before immediately apologizing. “I was going to say, ‘Ted Cruz,’ then decided not to because he’s out of the race,” Fiore, the Pulitzer-winning political animator, later told The Post’s Comic Riffs.

The slip was fitting, though, because just blocks from both the White House and an under-construction Trump Tower, the evening’s chatter from the stage couldn’t help but keep flowing back to Trump. Once he was declared “the Name That Must Not be Spoken” by Fiore, that would-be moratorium only seemed to increase the tendency to mention the presumptive GOP nominee for president.

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It’s only a matter of time till Trump would leave us for a younger country, said Shields, the PBS NewsHour political analyst who gave this year’s lecture — a talk previously given by such journalistic and political figures as Ben Bradlee, Bob Woodward, Garry Trudeau and then-senator Barack Obama.

Later, during an audience Q&A with both the cartoonist and the columnist, Shields said that Trump “is indifferent to facts” and an “opposition-research buffet.” But then he allowed: “I don’t know what his Achilles’ heel is” politically.

But the night was not only about Fiore, the Bay Area-based artist who in 2010 became the first Pulitzer winner to receive the Editorial Cartooning prize for an all-animation portfolio. The spotlight must rightly be shared each year with Herblock, the legendary Washington Post cartoonist whose foundation makes the Herblock Prize and other projects and exhibits possible. The Library of Congress is home to about 14,000 Herblock original artworks.

In terms of partisanship, Shields underscored that the left-leaning Herblock would strafe officeholders all along the political spectrum. In the ’90s, for instance, Herblock received the Medal of Freedom from President Bill Clinton. During the same administration, Herblock would draw Clinton with his trousers around his ankles, noted Shields, who for years worked at The Post as a “next-door neighbor” to Herb Block.

Both men were fitting choices to speak on this night about Herblock, in part because their experiences were from opposite perspectives. Fiore met Herblock just once, about two decades ago, when he came to The Post newsroom with his “terrible” portfolio in one hand and his copy of the legend’s recent book, “Herblock: A Cartoonist’s Life” (1993) in the other, he recounted. When he asked Herblock for career advice about getting a job in cartooning, the Post icon said he had no idea, pointing out: “I’ve had the same job since Eisenhower.”

But what a job Herblock did at midcentury and after, said Shields, especially in opposing Sen. Joseph McCarthy. “McCarthy had begun intimidating the political world,” Shields said. “Three weeks after McCarthy hit like a storm, there was a cartoon that would capture” the political reality: A Republican elephant being dragged to 11 tar buckets of “McCarthyism” (a term that Herblock famously coined).

“McCarthy wouldn’t have fallen,” Shields said he was convinced, “it it weren’t for Herblock.”

“He was a one-man search engine” for information,” said Shields of the Post cartoonist, who “stood up against brutes and bullies” — including Hitler as far back as 1932 — and “answered only to his integrity.”

[Cartoonists pay tribute to Herblock a decade after his death]

Fiore said that he, like Herblock, got into political cartooning not to make money, but rather to make a difference.

“I’m not trying to make [politicians] quake in their boots … ,” said Fiore, deftly avoiding mention of both the names Trump and Clinton. “I’m trying to put my thumbprint on the discourse.”