President Trump turned professional sports into a political battleground Friday and Saturday, directing his ire toward African American athletes who have spoken out against him and prompting a sharp rebuttal from the National Football League and the two most prominent basketball players in the world.

In a span of roughly 12 hours, as the sports world would typically be gearing up for college football and baseball’s pennant races, Trump agitated the most powerful sports league in North America and angered NBA superstars Stephen Curry and LeBron James.

At a political rally Friday in Huntsville, Alabama, Trump called on NFL owners to release players who demonstrated during the national anthem in the manner of former San Francisco 49ers quarterback Colin Kaepernick, who knelt last season to draw attention to police violence against African Americans.

Saturday morning on Twitter, Trump rescinded a White House visit invitation to Curry of the NBA champion Golden State Warriors, although it was unclear whether the Warriors had been invited in the first place.

“Going to the White House is considered a great honor for a championship team. Stephen Curry is hesitating, therefore invitation is withdrawn!” Trump posted.

The tweet followed comments he made Friday night at a rally for Republican Sen. Luther Strange, who is running in a special primary election to remain in the seat vacated by Attorney General Jeff Sessions.

“Wouldn’t you love to see one of these NFL owners, when somebody disrespects our flag, to say, ‘Get that son of a bitch off the field right now. Out! He’s fired. He’s fired!'” Trump said. “You know, some owner is going to do that. He’s going to say, ‘That guy that disrespects our flag, he’s fired.’ And that owner, they don’t know it (but) they’ll be the most popular person in this country.”

Saturday afternoon, Trump doubled down on Twitter.

“If a player wants the privilege of making millions of dollars in the NFL, or other leagues, he or she should not be allowed to disrespect our Great American Flag (or Country) and should stand for the National Anthem,” Trump wrote. “If not, YOU’RE FIRED. Find something else to do!”

NFL Commissioner Roger Goodell, who has waffled in either supporting or decrying Kaepernick, responded to Trump Saturday morning.

“Divisive comments like these demonstrate an unfortunate lack of respect for the NFL, our great game and all of our players, and a failure to understand the overwhelming force for good our clubs and players represent in our communities,” Goodell said.

NFL owners collectively donated more than $7 million to Trump’s presidential campaign, and New England Patriots owner Robert Kraft gave Trump a Super Bowl ring this summer.

“In calling upon his NFL ownership cronies to ‘fire the SOBs,’ he has effectively thrown these owners under the bus in exchange for a moment of applause in Alabama,” said Harry Edwards, a sociology professor at the University of California Berkeley. “Every owner, and especially the seven who supported him with both money and public association, are going to have to answer the questions, ‘What side of history are you on? Do you agree with Trump?’ If they agree or have no comment, they will be aligned against both the NFL commissioner and league office and the NFLPA. If they do not agree with his Alabama statements, they will in effect have separated themselves from both Trump and his alt-right constituency.”

Once again, Trump has placed himself at the center of a wrenching national debate over race. But unlike past presidents who have given at least some voice to a desire to bridge the historic divides in American life, Trump seems eager to lean in to those disputes.

For years as a private citizen, Trump was the most vocal proponent of the falsehood that President Obama was not born in the United States, a racially tinged conspiracy theory that thrived in fringe corners of the right. And during the presidential campaign, he was accused by his opponents of using his social media account to amplify anti-Semitic and racist voices.

After white supremacists and neo-Nazis descended upon Charlottesville, Virginia, to rally in favor of preserving Confederate monuments, Trump argued that the violence that ensued was the result of “both sides,” including counterprotesters who had taken to the streets to oppose the racist marchers.

After Trump said he rescinded Curry’s invitation, LeBron James slammed Trump on Twitter. He tweeted “U bum @StephenCurry30 already said he ain’t going!” James said. “So therefore ain’t no invite. Going to White House was a great honor until you showed up!”