In a pair of early-morning tweets, President Donald Trump once again encouraged football fans to boycott the NFL if the league does not “fire or suspend” players who kneel during the national anthem to protest racism.

Trump argued that if fans take coordinated action, they “will see change take place fast.”

If NFL fans refuse to go to games until players stop disrespecting our Flag & Country, you will see change take place fast. Fire or suspend! — Donald J. Trump (@realDonaldTrump) September 24, 2017

He went on to argue that the protests were partially responsible for what he asserted was declining public interest in NFL games.

...NFL attendance and ratings are WAY DOWN. Boring games yes, but many stay away because they love our country. League should back U.S. — Donald J. Trump (@realDonaldTrump) September 24, 2017

With the Twitter posts, Trump’s escalated his public campaign against the protests by athletes that he began with comments at a political rally in Alabama on Friday. “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, he’s fired?’” Trump said at the gathering.

His comments prompted an outpouring of criticism of Trump from several NFL players. And on Sunday the owner of one of the league’s most successful franchises joined that chorus. The New England Patriots ― the reigning Super Bowl champions ― released a statement from owner Robert Kraft, a friend and supporter of Trump’s, condemning Trump’s attacks.

“I am deeply disappointed by the tone of the comments made by the president on Friday,” Kraft said. “I am proud to be associate with so many players who make such tremendous contributions in positively impacting our communities.”

Kraft added that he backed the rights of players “to peacefully affect social change and raise awareness in a manner that they feel is most impactful.”

Statement from #Patriots Chairman & CEO Robert Kraft: pic.twitter.com/f5DJeK0Woj — New England Patriots (@Patriots) September 24, 2017

Shortly afterward, Jacksonville Jaguars owner Shad Khan locked arms with players and staff who knelt during the national anthem at the start of a game against the Baltimore Ravens in London.

Never seen an owner taking part in an anthem demonstration with players. But there is #Jaguars owner Shad Khan locking arms with players — Ian Rapoport (@RapSheet) September 24, 2017

NFL Commissioner Roger Gooddell on Saturday condemned Trump’s “divisive comments,” but refused to name him explicitly. And Miami Dolphins owner Stephen Ross also criticized the president’s “divisiveness” without naming him.

Trump’s crusade against the practice of kneeling during the national anthem began with his seemingly off-the-cuff remarks Friday at a rally on behalf of Sen. Luther Strange (R-Ala.), who is locked in a close race to hold onto his seat.

The president on Saturday tweeted that “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. If not, YOU’RE FIRED. Find something else to do!”

Aaron Bernstein / Reuters President Donald Trump at the rally in Alabama on Friday where he began his attacks on athletes who protest racism by kneeling during the playing of the national anthem.

Trump appears to be wagering that a prolonged battle over a hot-button cultural issue like the protests will work in his political favor. Treasury Secretary Steve Mnuchin defended Trump’s remarks in an interview on ABC’s “This Week,” telling host Martha Raddatz that players “have the right to have the First Amendment off the field,” but that the NFL should fine or suspend players who protest as the anthem is played at the start of games.

Trump’s attacks on protesting NFL players is part of a larger battle he and his administration has been having with the sports world. White House press secretary Sarah Huckabee Sanders suggested earlier this month that ESPN should fire host Jemele Hill for calling Trump a “white supremacist.”

On Saturday, Trump claimed he was withdrawing an invitation to the White House for the Golden State Warriors, the reigning NBA champions, because star guard Stephen Curry was “hesitating” about attending. Curry had said on Friday that he would vote against the team making the traditional visit, but that the Warriors had not yet decided as a group what to do.

Rather than have a chilling effect on athletes protesting racism, Trump’s comments have prompted a show of solidarity from many black athletes and entertainers, as well as white allies. NBA star LeBron James of the Cleveland Cavaliers spoke out against Trump, and on Saturday, Oakland Athletics catcher Bruce Maxwell became the first Major League Baseball player to kneel during the anthem.

The movement to protest racism, and particularly police killings of black men, by kneeling during the anthem began with a protest by then-San Fransciso 49ers quarterback Colin Kaepernick in an August 2016 pre-season game. Initially, Kaepernick sat during the anthem, but quickly switched to kneeling in a bid to avoid appearing disrespectful.

Kaepernick continued the protest through the 2016 season, inspiring many of his fellow players to join him. In March, Kaepernick opted out of his contract with the 49ers and has since failed to get picked up by another NFL team, leading to speculation that owners have blackballed him for his political stance.

This story has been updates with comment by Mnuchin and background on the escalating war between Trump and parts of the sports world.