Trump took time from a Twitter rant against criticism of the federal response to hurricane damage in Puerto Rico to tweet: "Very important that NFL players STAND tomorrow, and always, for the playing of our National Anthem. Respect our Flag and our Country!"
Protesting during the playing of "The Star-Spangled Banner" began 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.
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 congressional Republicans to repeal and replace the nation's health care law, the primary loss in Alabama of Trump's favored candidate, a turbulent hurricane season and the back-and-forth between the US and North Korea over missiles and nuclear weapons.