President Trump is feuding with the NFL. He argued that players shouldn’t take a knee during the national anthem to protest police violence against African-Americans. Trump also urged NFL team owners to do something to stop them. It’s possible that Trump is reading the results of polls showing that most Americans disapprove of the players’ protests and that he believes he can take political advantage of a cultural divide. And he may be right — for now.

We don’t have any polling specifically about Trump’s recent NFL comments, but a Quinnipiac University poll from 2016 found that only 38 percent of those surveyed approved of players choosing not to stand during the anthem. But while these NFL protests may be unpopular right now, particularly with white people, similar protests in the past — involving race, civil rights and varying definitions of patriotism — came to be viewed much more positively after the fact.

Marches for civil rights during the 1960s were generally seen negatively at the time. As the Washington Post noted last year, most Americans didn’t approve of the Freedom Riders, the March on Washington in 1963 or other similar protests. In fact, many Americans thought that these protests would hurt the advancement of civil rights. In addition, but many Americans held mixed-to-negative views of civil rights leader Martin Luther King Jr. In a 1966 Gallup survey, 63 percent of Americans gave King a negative score on a scale from -5 to +5. Now, the civil rights marches are viewed as major successes, and just 4 percent of Americans rated King negatively on that same scale in a 2011 Gallup poll.

Many Americans also viewed gay rights marchers during the AIDS epidemic negatively. According to Business Insider, the March on Washington for Lesbian, Gay and Bi Equal Rights and Liberation in April 1993 drew more than 800,000 people fighting against discrimination and seeking more funding for AIDS research. But in a Newsweek survey conducted at the time, only 23 percent of Americans thought that the demonstration did more good than harm in the fight for gay rights. Today, gay rights organizations celebrate the march, same-sex marriage is legal and much of the platform demanded by protesters seems mainstream.

The polling on the marches for black and gay civil rights underscores a fundamental truth about surveys: They merely measure how people feel at the time the polls are conducted. People can change their minds later. Civil rights protests, moreover, tend to involve a minority making demands of society at large, and so by definition begin as “unpopular” — which means that their initial unpopularity doesn’t tell us much about how they’ll ultimately be viewed.

The other lens through which to view the anthem protests — the lens Trump has used — is that they are un-American. But here, too, public opinion can shift. The Vietnam War provides a stark example. It’s now viewed as a mistake in which government officials misled the American public. During the Vietnam protests in the late 1960s, though, most Americans didn’t feel that way. Some 500,000 people marched on Washington on Nov. 15, 1969. Just 19 percent of Americans approved of these marches, according to a November 1969 CBS News poll. A whopping 77 percent disapproved of the protests. In other words, the current protests being held during the national anthem are far more popular than some of the marches conducted during the height of the Vietnam War.

But you don’t have to go back 50 years years to find a major war protest that Americans reversed themselves on. In the lead-up to the Iraq War, millions of people around the globe took to the streets to march against it. Most Americans (58 percent) disagreed with the viewpoints the protesters were articulating, according to a January 2003 Gallup poll. In fact, a minority (26 percent), including some who agreed with the protesters’ goals, said they shouldn’t even be marching. Then the actual war got under way and thousands of soldiers began dying. After just two years at war, Gallup found that a majority of Americans fairly consistently thought the war a mistake.

Of course, it’s far from guaranteed that views of the current athletes’ protests will change. Sometimes a lot of people march for a cause that is ultimately forgotten. Few probably remember the Solidarity Day march in Washington, even though a quarter of a million Americans attended it. It was staged in protest of President Ronald Reagan’s firing of 12,000 striking air-traffic controllers. A majority of Americans backed Reagan in that dispute, and the air traffic controllers’ strike is still seen as unsuccessful.

Still, the national anthem protests could be seen differently in the weeks and months ahead. Already, the players have picked up the support of personalities across the NFL after Trump launched his verbal barbs over the weekend. They included coaches, owners (many of whom backed Trump in the 2016 presidential campaign) and even the commissioner, who issued a statement opposing Trump’s remarks.