NASCAR driver Dale Earnhardt Jr. on Monday quoted John F. Kennedy on "violent revolution" after President Trump attacked National Football League (NFL) players who kneel during the national anthem.

"All Americans R granted rights 2 peaceful protests," he tweeted Monday.

"Those who make peaceful revolution impossible will make violent revolution inevitable-JFK."

All Americans R granted rights 2 peaceful protests

Those who make peaceful revolution impossible will make violent revolution inevitable-JFK — Dale Earnhardt Jr. (@DaleJr) September 25, 2017

In response to another tweet telling him to be careful when commenting on these issues, Earnhardt said he agrees it's a complex issue, before adding: "But some team owners spoke on this."

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His comments come after Trump last week attacked NFL players who refuse to stand during the national anthem.

On Sunday, many players across the country knelt or locked arms during their first games since Trump's comments.

Several NASCAR team owners said Sunday they wouldn't condone drivers protesting during the national anthem.

Former NASCAR champion Richard Petty told The Associated Press that any member of his team would be fired if they chose to protest the national anthem.

Trump on Monday said he was "proud" of NASCAR, its supporters and its fans.

"They won't put up with disrespecting out Country or our Flag," Trump tweeted. "They said it loud and clear!"

So proud of NASCAR and its supporters and fans. They won't put up with disrespecting our Country or our Flag - they said it loud and clear! — Donald J. Trump (@realDonaldTrump) September 25, 2017

Trump on Monday also tweeted that fans who booed players who kneeled during the national anthem were demanding respect for the country's flag.

He said the issue of kneeling isn't about race, but is instead about respect for the country and its flag.

"NFL must respect this!" Trump tweeted.