U.S. President Donald Trump tweeted a new campaign ad on Wednesday, just less than a week before the U.S. midterm elections, which has instantly been dubbed the most racist ad in a generation.

The ad, which Trump pinned to the top of his Twitter account, opens with the line, "Illegal immigrant, Luis Bracamontes, killed our people!"

"Democrats let him stay," the ad then claims.

"It is outrageous what the Democrats are doing to our Country. Vote Republican now!" the president tweeted alongside the ad.

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The man featured in the incendiary ad is Luis Bracamontes, a Mexican citizen who entered the U.S. illegally and was sentenced to death for the murder of two Sacramento County sheriff's deputies.

The ad then shows Bracamonts, being led out of court, saying that he wants "to kill more cops soon." It then concludes with the question, "Who else would Democrats let in?"

Republican Arizona Senator Jeff Flake, a Trump critic, reportedly said, "This is just a new low in campaigning. It's sickening," while Democratic National Committee Chairman Tom Perez told CNN the add is "dog whistle politics" based on "fear-mongering."

Many critics compared the ad to President George H.W. Bush's 1988 Willie Horton ad, which depicted a violent criminal who had been paroled by Bush's Democratic opponent Michael Dukakis.

Responses to the ad on Twitter ranged from shock to instant condemnation to what many saw as racist rhetoric used to incite hate and rally Trump's base. Eric Umansky, Deputy Managing Editor or ProPublica, wrote that, "Thirty years ago, George H.W. Bush released his infamous fear-mongering, racist ad on Willie Horton. This Trump ad is worse. Far worse."

Trump sends troops to the border

Trump on Wednesday also said the number of military troops deployed to the U.S.-Mexican border could reach 15,000 — roughly double the number the Pentagon said it currently plans for a mission whose dimensions are shifting daily.

The Pentagon says “more than 7,000” troops were being sent to the southwest border to support the Customs and Border Protection agents. Officials said that number could reach a maximum of about 8,000 under present plans.

The troop numbers have been changing at a dizzying pace, with Trump drawing a hard line on immigration in the lead-up to the midterm elections.

Just last week officials were indicating that about 800 to 1,000 might be sent. On Monday, officials announced that about 5,200 were being deployed. The next day, the Air Force general running the operation said more than the initially announced total were going, and he pointedly rejected a news report that it could reach 14,000, saying that was “not consistent with what’s actually being planned.”

Gen. Terrence O’Shaughnessy, the commander of U.S. Northern Command, told reporters the number would exceed the initial contingent of 5,200, but he offered no estimate of the eventual total.

Just 24 hours later, Trump thrust new uncertainty into the picture, catching the Pentagon by surprise.

The Associated Press contributed to the report