The 1960s and ’70s saw a hurricane of political athletes: legends like Muhammad Ali, John Carlos, Tommie Smith, Curt Flood, and Billie Jean King. But nothing, literally nothing, in the history of sports and politics can compare to what happened on Sunday.

Expressions of dissent broke out in every single NFL game during the playing of the national anthem. Some players kneeled, some sat, some raised fists, and some linked arms. But all of them were standing in opposition to Donald Trump. Announcers and commentators discussed their actions sympathetically. The booing one might expect from fans was sparse. Two anthem singers—a black man in Detroit and a white woman in Tennessee—took a knee during the last note of the song. How did this happen? How did the sport that—from ownership down—has historically been associated with the most conservative politics see this maelstrom of united discontent?

It starts with Colin Kaepernick, and it ends with understanding the “brotherhood” that exists in NFL locker rooms. Kaepernick, of course, is the blackballed (or whiteballed) free-agent NFL quarterback who took a knee and protested during the anthem last season to highlight the issue of police violence. I can say unequivocally from my reporting that, while only a small group of NFL players joined Kaepernick in this protest last season, the respect he garnered throughout the community of players for doing it week after week for four straight months, weathering all kinds of brutal criticism, was deep. Kaepernick lit the match. It was kept alight earlier this season by players like Seattle Seahawk Michael Bennett, Philadelphia Eagle Malcolm Jenkins, Oakland Raider Marshawn Lynch, and a dozen members of the Cleveland Browns and others, but the gasoline was poured upon this flame by Donald Trump on Friday. People no doubt are aware of what should be known as “the Alabama speech,” in which he called for protesting NFL players to be fired and referred to anyone who protested as a “son of a bitch.”

This is where we get to the question of solidarity. Donald Trump never played football, and therefore does not understand what Bennett calls “the brotherhood.” Football players are very tight-knit as a community. It’s certainly not always a positive solidarity, most pointedly seen in the reticence of players to speak out when a teammate commits an act of violence against women, as well as in the pressure to play when hurt, which often comes from your “brothers,” not coaches. But this “brotherhood” also means that when someone threaten the livelihoods of the players and disrespect their families, they will stand as one.

From Trump’s perspective—leader of, as former NFL player Adalius Thomas called it in a scathing critique of Trump on MSNBC, “The Divided States of America”—these players probably seemed like a smart target. Trump reserves his greatest venom for black people and women—as we have seen time and again—and certainly thought that going after wealthy black athletic dissenters was a clever move. But it didn’t line up as he had hoped. First the union came out strongly in defense of players and challenged management to do the same. Then team owners and Roger Goodell came out—far less strongly, but still making it perfectly clear what side they were on. Even though their comments were not exactly fiery, they stood with the dissenting players. This matters, when we consider just how many of these owners supported Trump in the campaign. (If they were truly on the side of angels, not to mention meritocracy, they wouldn’t just talk the talk, but they’d sign Colin Kaepernick.)

Then this tumult spilled over into the Sunday morning shows. People like former NFL player Anquan Boldin had a platform on ABC News to say, “I don’t like the hate speech that is coming out of [Trump’s] mouth. Neither do the players in the locker room.”

Seahawk wide receiver Doug Baldwin shamed Trump with a statement so eloquent one wondered why he couldn’t be president.

Then there was the declaration of the entire Seahawks organization, on team letterhead, which read, “As a team we have decided we will not participate in the national anthem. We will not stand for the injustice that has plagued people of color in this country. Out of love for our country and in honor of the sacrifices made on our behalf, we unite to oppose those that would deny our most basic freedoms. We remain committed in continuing to work towards freedom and equality for all.”

But even beyond these voices, there was also Fox announcer—and Southern NFL icon—Terry Bradshaw, who said, “Not sure if our president understands those rights, that every American has the right to speak out and also to protest.”

Then there was former NFL coach Rex Ryan, a vocal Trump supporter who campaigned for the man. He said, “I’m pissed off I’ll be honest. I supported Trump, and I’m appalled at these comments. SOBs? Not the men that I know.”

One could certainly be forgiven for wondering what Trump he was watching during the campaign. But all of it speaks to the very intense, if at times deeply distorted, sense of solidarity that exists throughout the league at every level.

This is what Trump lacked the capacity to understand—and the divider in chief painted himself into a corner. For one day, the NFL was united.

The line of the day that explained it all was said by ESPN NFL commentator and future Hall of Famer Charles Woodson. He said, “This is choose-your-side Sunday. It really is. And what side are you on?”

When it comes to the NFL, that “side” does not involve standing with Donald Trump. In the 1960s, athletes made history. On Sunday, a new link was forged.