Chris Christie may have thought he was paying Sen. Cory Booker (D-N.J.) a compliment by calling him “articulate,” but many Twitter users saw it as a dog whistle.

Booker announced Friday that he was running for the 2020 Democratic presidential nomination. Considering they are both New Jersey politicos, it was a natural topic for Christie to discuss at an event hosted by The Washington Post the same day.

Christie actually thinks Booker could be a threat to Trump’s re-election prospects.

“Cory Booker: talented, smart, articulate, hope that he stays in this campaign to the roots that I saw him establish in New Jersey,” Christie said. “He was someone who was pro-voucher, he was pro-charter school, he was somebody who was tough on crime in the city of Newark. If he stays in that lane, and is the articulate, inspirational guy that he is, then I think he’s got a legitimate chance to be a serious potential problem for the president in the general election.”

The former New Jersey governor made it clear he liked Booker, but his use of the word “articulate” came across as a patronizing, backhanded compliment.

As AlterNet noted:

“Articulate” is rarely a term applied to anyone besides notable people of color, and it conveys a presumption that the typical black man would not speak very intelligently.

During the primary stages of the 2008 presidential campaign, Joe Biden came under fire when he praised then-opponent Barack Obama as “the first mainstream African-American who is articulate and bright and clean and a nice-looking guy.”

Obama still chose Biden as his running mate.

Many Twitter users also noted that Christie’s compliment came across as a dog whistle: