Donald Trump, left, and Brandon Stanton, right.

In just three days, photographer Brandon Stanton's open letter to Donald Trump has become one of the most-shared Facebook posts in the history of the social network -- by some reports the most-shared single post of all time.

Stanton is the shutterbug behind the wildly popular blog Humans of New York, in which he publishes portraits of Gotham's residents along with brief interviews. In what he calls his first political post ever, he says that speaking out against the Republican presidential candidate—who has advocated for torture, urged violence by his supporters, and branded Mexican immigrants rapists—is a moral duty.

As of Thursday morning, Stanton's "open letter" had been shared upward of one million times, and has topped two million "reactions" from people including Hillary Clinton (or from whoever is in charge of Clinton's Facebook presence).

By comparison, the most shared post of 2015 was a photo of a child who had beaten cancer, according to the analytics site CrowdTangle. That post has racked up 622,000 shares over the last 12 months. Stanton's post has garnered upward of 50 percent more shares—in just three days.

artnet

The Donald has inspired an outpouring of anti-Trump creativity among artists. Among those that have made headlines in recent weeks: street artist Hanksyportrayed him as a pile of excrement; "gender fluid Futurist" Illma Gore depicted himwith a tiny sex organ; and Phillip Kremer posts distorted images of him on Instagram.

Here's Stanton's letter to the man who is, let's remember, the leading contender for the Republican presidential nomination:

artnet