"So proud of NASCAR and its supporters and fans," Trump wrote on Twitter at 7:25 a.m. ET. "They won't put up with disrespecting our Country or our Flag - they said it loud and clear!"
He went on to write eight minutes later: "Many people booed the players who kneeled yesterday (which was a small percentage of total). These are fans who demand respect for our Flag!" He later tweeted "#StandForOurAnthem" and retweeted a user who cited for NFL player Pat Tillman, who was killed in Afghanistan in 2004 while serving with the Army Rangers.
In a statement released Monday afternoon, NASCAR said sports are a "unifying influence in our society."
"Our respect for the national anthem has always been a hallmark of our pre-race events. Thanks to the sacrifices of many, we live in a country of unparalleled freedoms and countless liberties, including the right to peacefully express one's opinion," the statement said.
Dale Earnhardt Jr., arguably NASCAR's biggest star, defended the right to protest in a tweet.
"All Americans R granted rights 2 peaceful protests / Those who make peaceful revolution impossible will make violent revolution inevitable-JFK," he wrote on Twitter.
Trump's message praising America's foremost auto racing circuit came after widespread demonstrations at football games over the weekend, prompted by Trump's repeated calls to fire players who kneel during the national anthem. Several NASCAR team owners said over the weekend
they wouldn't tolerate a similar movement in their sport.
The rancor began Friday evening, when Trump used an expletive to describe players who took part in protesting the anthem during a campaign rally in Alabama. He threw gasoline on the flames Saturday and Sunday, writing on Twitter that the league was suffering a decline in viewership because of the political protests.
His remarks struck many as stoking racial resentments because the players he criticized were black and their protests were meant to highlight racial injustice. But Trump told reporters his objections had nothing to do with race.
Departing New Jersey, where he had spent the weekend at this Bedminster golf club, Trump said his comments had "nothing to do with race or anything else — this has to do with respect for our country and respect for our flag."
He sought to underscore that point Monday morning, writing on Twitter: "The issue of kneeling has nothing to do with race. It is about respect for our Country, Flag and National Anthem. NFL must respect this!"
But his praise of NASCAR will do little to quiet the suggestion that Trump is, at least implicitly, fueling a racial issue. While many of the most prominent players in the NFL and the NBA are black, auto racing has long been viewed as the whitest of professional American sports. Even as other leagues -- like those for golf and tennis -- have seen black athletes rise to stardom, NASCAR has remained dominated by white drivers.
When he raced in NASCAR's top national series this summer, Darrell "Bubba" Wallace Jr. became the first black driver to compete at that level since 2006. He was only the fourth black driver to compete at that level for NASCAR since 1961.
For decades it was not uncommon to see the Confederate flag waved at NASCAR tracks, though the sport's governing body took steps in 2015 to rid its events of the symbol.
Television ratings have been declining for NASCAR over the past decade, as they have for the NFL.