WASHINGTON — Extensive work was well underway on a new $20 bill bearing the image of Harriet Tubman when Treasury Secretary Steven Mnuchin announced last month that the design of the note would be delayed for technical reasons by six years and might not include the former slave and abolitionist.

Many Americans were deeply disappointed with the delay of the bill, which was to be the first to bear the face of an African-American. The change would push completion of the imagery past President Trump’s time in office, even if he wins a second term, stirring speculation that Mr. Trump had intervened to keep his favorite president, Andrew Jackson, a fellow populist, on the front of the note.

But Mr. Mnuchin, testifying before Congress, said new security features under development made the 2020 design deadline set by the Obama administration impossible to meet, so he punted Tubman’s fate to a future Treasury secretary.

In fact, work on the new $20 note began before Mr. Trump took office, and the basic design already on paper most likely could have satisfied the goal of unveiling a note bearing Tubman’s likeness on next year’s centennial of the 19th Amendment, which granted women the right to vote. An image of a new $20 bill, produced by the Bureau of Engraving and Printing and obtained by The New York Times from a former Treasury Department official, depicts Tubman in a dark coat with a wide collar and a white scarf.