The ad shows old courtroom footage of Luis Bracamontes, an illegal immigrant who was accused of killing two Sacramento, California-area sheriff's deputies in 2014 (he was convicted and given the death penalty this past April), and it attempts to link him to the Central American migrant caravan that Trump has been characterizing as an "invasion".
The video is eerily reminiscent of the infamous 1988 "Willie Horton" ad used by supporters of the George HW Bush campaign against Democratic presidential candidate Michael Dukakis and condemned as racist.
The new ad, tweeted Friday by Trump campaign manager Brad Parscale, warns ominously that a caravan of migrants that has been traveling toward the USA could be filled with "dangerous illegal criminals".
"Thirty years ago, George H.W. Bush released his infamous fearmongering, racist ad on Willie Horton", Eric Umansky, deputy managing editor of ProPublica, a U.S. non-profit newsroom, tweeted.
The video tweeted by Trump did not immediately appear to be running on television - it has a runtime longer than most TV ads - although it received extensive coverage on cable news networks.
Clips from the same Bracamontes court session appear in both ads, both feature menacing music straight out of the political-attack-ad playbook, and both serve up exactly the same message: that the Democrats are welcoming murderous immigrants into our country. It adds: "Democrats let him into our country ..." It includes scenes of a migrant caravan moving toward the US, warning ominously, "Who else would Democrats let in?" and suggesting that more violence would soon penetrate the border. As of Thursday afternoon, it had received 3.51 million views in less than 24 hours and was the "pinned" tweet atop Trump's profile, meaning it was the first thing any visitor to his Twitter page would see.
Republican senator Jeff Flake called the advert "sickening", saying "Republicans everywhere should denounce it".
Tom Perez, chairman of the Democratic National Committee, called the new ad the "dog whistle of all dog whistles". And Rep. Carlos Curbelo, R-Fla., seeking re-election in a Democratic-leaning South Florida district, said he'd not seen the video but criticized Trump's use of it.
"This is distracting, divisive Donald at his worst", Perez said on CNN.
The immigrant living in the country illegally sports a shaved head and long chin hair. Bracamontes also starred in a Trump ad released in January, titled "Complicit", in an effort to drum up support for the border wall. During his 2016 campaign, he frequently appeared with so-called "angel families" - those who lost loved ones at the hands of immigrants in the nation illegally.