On Sunday, Strong hand-delivered the manure to two Los Angeles homes he believed belong to Mnuchin - one in Beverly Hills, and one a mansion in Bel Air that consequently got a visit from Secret Service agents and a bomb squad.
"I wanted to ring the door and hand it to him myself," Strong told AL.com the next day, after his early Christmas package had locked down one of the richest neighbourhoods in the world.
Strong works as a psychologist for Los Angeles County, he told 89.3 KPCC, and expects that delivering animal feces to the man in charge of the US Treasury Department could jeopardise his job.
But Strong doesn't sound as if he regrets it.
"I need someone to ride along and document my Secret Santa project. I'm going to hand deliver boxes of horse (expletive) to Steve Mnuchin," he wrote on Facebook on Sunday, a couple of hours before police were called to Bel Air.
"No disguises, no fake names. Totally owning this one. You're only powerless if you do nothing!!!"
As proof of his commitment, he posted photos of himself - shovel in hand, serene smile beneath his beard - loading manure into a box the size of a mini-fridge.
It looked much like the box a news helicopter would later observe being dumped out by police in Bel Air, as so many police and federal agents swarmed the street that Mnuchin's neighbors couldn't leave their driveways.
"We have US$50 million homes and we can't move," complained the widower of Zsa Zsa Gabor. "They have to find another way."
But to Strong, this was the perfect way to express his outrage over a bill signed last week that is expected to massively increase the deficit by cutting taxes for most Americans - especially corporations and the rich.
"In the long run, if we don't do stuff like this, what are we going to have left?" Strong told KPCC. "What I did, I would like to compare to what Jesus did when he went into the temple and overturned the tables of the money-changers, who were exploiting the people financially in the name of religion.
"I feel like that's what the GOP has done to the American people."
Even before he pushed for the tax bill, Mnuchin symbolised wealthy entitlement to many critics of President Donald Trump's Administration. The financier is worth hundreds of millions of dollars. Since becoming Treasury Secretary, he has battled reports that he requested a government jet for his honeymoon and used a government plane to fly to Fort Knox and watch a solar eclipse.
It's unclear whether Mnuchin was home as police stood outside a neighbour's house and dumped animal feces all over the ground. Neither LAPD nor the Secret Service have commented on the investigation.
In any case, authorities soon determined that the package contained no explosives and departed from Bel Air.
"LOL!" Strong wrote on Facebook. "It was pure organic horse--, just like everything that administration's done so far. Bomb scares certainly were not my intention, but maybe they should be a little scared, eh."
His escapade earned him a visit from Secret Service agents yesterday, Strong said. But he wasn't arrested, and he subsequently compared himself to another man who ended up on the wrong side of the federal government: Martin Luther King.
That said, few would confuse the rhetoric of the civil rights leader - or Jesus Christ, for that matter - with the messages of Robby Strong, self-professed manure elf.
"It was a gift-wrapped package of poo," Strong told AL.com. "Is there a law that you can't drop off a box of poo? Not really."
