Dorothy A. Brown is a law professor at Emory University. The views expressed in this commentary are solely those of the author. View more opinion articles on CNN.

(CNN) President Donald Trump wants NASA to go to Mars, but his Treasury secretary can't figure out how to put Harriet Tubman on the $20 bill?

Dorothy A. Brown

We recently learned that the planned Harriet Tubman currency — which was slated to replace the $20 Andrew Jackson bill in time for the 2020 centennial of the 19th Amendment — can't be rolled out until 2028. This, even though the engraving plate for it was completed "as recently as May 2018" a Treasury Department employee told the New York Times. The employee also said the design "appeared to be far along in the process," according to the Times. Apparently so — as we all saw a picture of it leaked to the press.

Pay no attention to that, Treasury Secretary Steven Mnuchin has indicated. There are technical difficulties and they will persist until long after President Trump leaves office, he tells us. We'll pause here to note that the plan for the Tubman bill originated with Trump's predecessor, the first black President of the United States. President Barack Obama referred to Harriet Tubman — an abolitionist who led enslaved people to freedom via the Underground Railroad — as "an American hero ... [who] fought tirelessly for the Union cause, for the rights of enslaved people, for the rights of women, and for the rights of all."

In 2016, candidate Trump told NBC that stripping his favorite president, the populist and slave owner, Andrew Jackson, from the $20 bill was " pure political correctness ." He suggested that Tubman be bumped to the $2 bill, which is no longer printed.

In the scheme of things, this is not the worst thing the President or his administration has done to disrespect a source of black pride, but it is telling. This President's belief in white supremacy knows no bounds and perhaps a better descriptor would be to start referring to him as our white-supremacist-in-chief.