President Donald Trump's comments about the NFL on Friday, in which he said owners should "fire" players for taking a knee during the national anthem, was not the first time he's leveled harsh criticism at the game. Trump has called the NFL "boring" on multiple occasions and claimed that ratings were down despite the NFL being the most watched television sport in the U.S.

Trump doubled down on his criticism Wednesday while on his way to Indiana.

"I think the NFL is in a box. I think they're in a really bad box," Trump told reporters. "You look what's happening with their ratings. Frankly, the only thing doing well in the NFL is the pregame because everybody wants to see what's going on.

"You cannot have people disrespecting our national anthem, our flag, our country, and that's what they're doing. And in my opinion, the NFL has to change. Or you know what's going to happen? Their business is going to hell."

Trump's history of personal battles with NFL owners dates back to the early 1980s when he tried to directly compete with the league as majority owner of the New Jersey Generals, one of 12 teams in the newly formed United States Football League. By 1986, the USFL would file an anti-trust lawsuit against the NFL and win, but the league received a token $1 in the judgment and then promptly folded.

Decades later, Trump said the USFL was "a good league." He later admitted that he was trying to become an NFL owner by forcing a merger between the two leagues.

"I would have liked to have been an NFL owner if I could have got in inexpensively," Trump said.

Trump was never able to own a team and has not been shy about voicing his bitterness. In an interview with the New York Times in 1984, Trump said he felt sorry for the "loser" who might buy the Dallas Cowboys, a team that is now America's most valuable sports franchise at $4 billion.

In 1988, Trump supposedly was approached by the owners of the New England Patriots about buying the team. The price tag came out to $85 million but he balked because he claimed the team had debt issues. The Patriots are currently the second-highest valued NFL franchise at $2.6 billion.

In 2014, Trump made an unsuccessful bid to purchase the Buffalo Bills and would later draw headlines for himself by denouncing the purchase by Terry Pegula, owner of the NHL's Buffalo Sabres. Trump posted on Twitter that he hoped for the sake of Buffalo fans that the Bills would do better than the Sabres and called the $1.4 billion price "ridiculous." Three years later, the Bills are valued at $1.6 billion, according to Forbes.

Two years ago, Trump told Sports Illustrated that he was happy to have lost out on the Bills because it freed him to run for president. "I'm glad, because if I bought the Buffalo Bills, I probably would not be doing what I'm doing now, which is much more important. I would have done a good job with the team, but I wouldn't be doing what I'm doing now."

In May 2015, Trump said Patriots quarterback Tom Brady should "sue the hell" out of the NFL for defamation after the Deflategate scandal.

"Two-hundred-and-fifty million dollars. Sue them Tom. They’ll settle so fast your head will spin," Trump said.

Trump's cabinet also has an anti-NFL element. Small Business Administration Administrator Linda McMahon previously served as president and CEO of World Wrestling Entertainment, which in 2001 competed against the NFL by starting a professional football league, the XFL. 

Like the USFL, the XFL folded quickly, lasting just one season.