WASHINGTON — President Donald Trump is putting pro football players on notice for Week 4 of the NFL season: He won’t stand for it if they kneel in protest during the national anthem.

At Sunday’s first game, in London, New Orleans Saints players, coaches and staff knelt before the start of the anthem but stood in unison once it began. On the Miami Dolphins’ sideline, three players were on one knee during the singing of “The Star-Spangled Banner.”

Amid a series of tweets Saturday against criticism of the federal response to hurricane damage in Puerto Rico, the president returned to the world of sports and society: “Very important that NFL players STAND tomorrow, and always, for the playing of our National Anthem. Respect our Flag and our Country!”

Very important that NFL players STAND tomorrow, and always, for the playing of our National Anthem. Respect our Flag and our Country! — Donald J. Trump (@realDonaldTrump) September 30, 2017

Protesting during the playing of “The Star-Spangled Banner” drew national attention last season when Colin Kaepernick, then a quarterback with the San Francisco 49ers, declined to stand as a way to bring attention to police treatment of blacks and to social injustice.

During a speech at a political rally in Alabama on Sept. 22, Trump called for NFL owners to fire players who engaged in such a protest. In the days that followed the president issued a series of tweets reiterating his views and calling for a fan boycott of games.

Criticism from players, owners and fans — and some praise — greeted Trump’s remarks.

The controversy boiled for days and seemed to overshadow other issues facing the Trump presidency, including the failure of Republicans to repeal and replace the nation’s health care law; the Senate primary loss in Alabama of Trump’s favored candidate; a turbulent hurricane season; and tensions over North Korea’s missiles and nuclear weapons.

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“I do really believe his heart’s in the right place,” House Speaker Paul Ryan, R-Wis., said on CBS’ “Face the Nation.”

“I think what matters is that we have to show people that we are an inclusive society, that we want everyone to succeed,” he said.

Ryan also acknowledged that the original point of the player demonstration — racial injustice and police mistreatment of African-Americans — has become obscured by the narrower issue of how to act during the anthem.

“I think we should just have separate and distinct conversations. Because when you merge it into the flag and the anthem, it’s lost,” Ryan said.

Relatively few players had demonstrated before Trump’s remarks. Last Sunday, more than 100 NFL players sat, knelt or raised their fists in defiance during the national anthem.