IT WAS the summer of 1968, and Garry Trudeau, home after a seasonal job in Washington, had a few days to kill before returning for his junior year at Yale. So he sat on his bed in Saranac Lake, N.Y., and began to draw; by the end of an afternoon, he had created a week of comic strips that would alter the entire direction of his life.

There, in incipient form, he rendered B.D., a quarterback character named as a nod to Yale football player Brian Dowling. This was a sports strip, Trudeau recounts, but B.D. and his teammates did more talking than tackling, with their Vietnam War-era huddle serving less as an arena for marching orders and more as a verbal playground for exchanging ideas.

The next week, Trudeau took his four-panel samples to the Yale Daily News, where executive editor Reed Hundt told the aspiring cartoonist: “They’re all right. We publish pretty much anything.” And so on Sept. 30 — 50 years ago this month — the characters of what would become “Doonesbury” first saw the light of publication, beginning what Trudeau calls his “life’s project.”

“A couple of months later, I was offered my current job,” Trudeau tells The Washington Post’s Comic Riffs. A couple of months later, too, Richard Nixon would be elected to his first presidential term.

The then-fledgling Universal Press Syndicate would officially launch “Doonesbury” in 1970. Within five years, Trudeau was picking up the Pulitzer Prize for editorial cartooning — the first comic strip ever to receive that honor — largely because of his satirizing of a stonewalling Nixon.

Now, on the 50th anniversary of the birth of B.D. and Mike Doonesbury in the student strip “Bull Tales,” Trudeau is finding much satirical fodder in another president mired in controversies and under investigation.

Trudeau has mocked Donald Trump for decades, with the real estate mogul-turned-TV host sometimes sniping back by calling Trudeau a “third-rate” cartoonist. That thick, sometimes prescient comic history spawned the best-selling “Doonesbury” collection “Yuge!” just before Trump’s election.

This week, Trudeau offers a follow-up treasury of Sunday strips in a collection titled “#SAD!: Doonesbury in the Time of Trump.” And reading the cartoonist’s fresh swipes at the White House — sometimes through such characters as radio talker Mark Slackmeyer and former Washington Post journalist Rick Redfern, who lived through the Nixon era — it is easy to see satiric parallels.

So having lampooned both eras, does Trudeau see ways in which the Trump and Nixon administrations are alike?

“The most similar, of course, is the corruption at the top — and the way the stain inexorably spread down into the ranks,” Trudeau says. “But let’s not leave out the Reagan administration, which still holds the record for sleaze — 138 officials investigated, indicted or convicted.”

That is “not how he’s remembered, of course,” he notes. “Being naturally sunny and disingenuous has its advantages.”

Trudeau — who will be in Washington on Oct. 1 to speak at Politics & Prose — is also willing to give credit to Nixon where he gives Trump none.

There are too many differences to list, the cartoonist says, but “let’s give a shout-out to a few big things that Nixon got right, like the creation of the EPA and the overture to China. If Trump has done anything to benefit anyone other than himself and a few special interests, it’s escaped me. Judges to protect corporations and tax cuts for the wealthy don’t count.”

Trudeau’s decades of studying Trump leaves him mostly unsurprised by how he has conducted his presidency.

“He’s always been pure id, utterly void of principle, so there’s been nothing unpredictable about the horror show,” Trudeau says. “It’s how well it’s worked for him that’s surprising. My mistake was not in underestimating Trump — it was overestimating the electorate.”

Trudeau also has keenly observed Trump’s strategic ability to hold the spotlight like no modern president before him.

“He’s unique, but humans are programmed to pay attention to things that inflict harm,” he says. “Fifteen seasons of reality TV taught Trump that treating people badly never gets old.”

Trudeau really began taking notice of Trump three decades ago, spoofing what he saw as the mogul’s sense of grandiosity and gilded pomposity. From early on, “Doonesbury’s” Trump character would boast about the “unbelievable, amazing public interest in my sex life,” and stir reader fascination with his political aspirations.

What has changed most about the character since the ’80s is the pate and the patter. Trudeau likes to say that he’s been trying to reverse-engineer Trump’s hair “ever since it was brown.” And “Doonesbury’s” President Trump seems to speak in even more clipped bursts of hyperbole than the character did decades ago. As Trudeau has said: “Drawing Trump is a journey, not a destination.”

Meanwhile, as Trudeau marks a golden anniversary, does he have a plan for how much longer he’ll continue to mock politicians through his now weekly “Doonesbury”?

“I’ve pretty much stopped thinking in terms of milestones,” the cartoonist says. “Anniversary years aren’t actually motivational for creativity. I’ll quit when it’s no longer fun.”

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