Minutes after Treasury Secretary Steven Mnuchin said Wednesday that he was delaying the new Harriet Tubman $20 bill until 2028, a New York designer tweeted: “We’ll see about that.”

Dano Wall, 33, has created a 3-D stamp that can be used to superimpose a portrait of Tubman over Andrew Jackson’s on $20 bills. Wall said he has sold out of the stamps and is hurrying to produce more.

“My goal is to get 5,000 stamps out there,” said Wall. “If there are 5,000 people consistently stamping currency, we could get a significant percent of circulating $20 bills with the Tubman stamp, at which point it would be impossible to ignore.”

Wall began manufacturing the stamps in 2017, soon after President Donald Trump took office, and Mnuchin refused to commit to the Obama administration’s plan to put Tubman on the 20.

Jackson, the nation’s seventh commander in chief, was a slave owner. Tubman, who escaped slavery on Maryland’s Eastern Shore, helped lead hundreds of people to freedom along the Underground Railroad.

Wall has been stamping as many $20 bills as he can and encouraging others to do the same. “Putting Harriet Tubman on the front of the $20 bill would have constituted a monumental symbolic change, disrupting the pattern of white men who appear on our bills,” he said, “and, by putting her on the most popular note currently in circulation, indicates exactly what kind of a life we choose to celebrate; what values we, as a country, most hope to emulate. Harriet Tubman’s unparalleled grit, intelligence, and bravery over the course of her long life certainly make her worthy of such an honor. “

Last month, Trump described the redesign of the $20 bill with Tubman’s image as “pure political correctness” and suggested she could be added to the $2 bill instead. Trump admires Jackson, the first populist to occupy the White House.

“Andrew Jackson had a great history,” Trump said, “and I think it’s very rough when you take somebody off the bill.”

But Jackson was also the president responsible for the 1830 Indian Removal Act, which forced more than 60,000 American Indians from their lands and onto the Trail of Tears.

In her book, “Unhinged,” former White House staffer Omarosa Manigault Newman wrote that when Trump was shown an image of Harriet Tubman, his response was: “You want me to put that face on the twenty-dollar bill?”

But Wall said the more he learned about Tubman, the more impressed he was.

“Before this project,” Wall said, “I knew she was a famous American, someone I looked up to in the vague sense without realizing everything she did in the Army. I since learned she was a spy for the Union. She was buried with military honors. She freed over 1,000 people. The more you learn about her, the more you are in awe of what she was able to accomplish.”

Wall said he’s been careful not to violate a U.S. law of defacing currency. “The basic gist of it is you can’t render a bill illegible,” Wall said. “You can’t cover any text or numbers or anything on it to serve as an advertisement. … Anything outside of that, if the bill is still fit for circulation, is fine. You can write on it and mark it in any way.”