The latest Gallup U.S. Daily survey yielded insights that ought to concern the National Football League.

Gallup finds that 57% of American adults say they are fans of pro football, down from 67% in 2012 when Gallup last asked the question. That’s a slide of 10 percentage points in just five years. Gallup surveyed 1,012 adults aged 18 or older on Oct. 10 and Oct. 11, by cellphone and landline. The margin of error is 4%.

Is it Trump and the player protests?

As every football fan is likely aware, President Donald Trump has vocally criticized the NFL, and NFL team owners, for the past two weeks for allowing players to protest during the playing of the national anthem.

Is it possible the decline in American pro football fans is directly related to the protests?

Gallup editor Jeffrey Jones is hesitant to pin it all on that. “The anthem situation is the latest, but not the only controversy that has dogged professional football,” he writes on Gallup’s website. “In recent years, the NFL has come under fire for its handling of domestic violence cases involving players and its response to research on the effects of concussions on brain health among former players.”

But additional insights from Gallup’s survey suggest the anthem controversy is having an impact. Republicans identifying as fans of pro football fell 15% and Independents fell 12%, while Democrats only fell by 3%.

That leaves what Gallup calls a “significant party gap” in NFL fans: 66% of Democrats and only 55% of Republicans identify as fans of pro football. Of course, it is possible that the gap is due to some other common reason felt more strongly by Republicans than Democrats, but the suggestion is that Republicans are outraged by the player protests, or at least following Trump’s lead, while Democrats are less so.

In a Yahoo Finance survey, 62% of NFL fans said they plan to watch less football this season because of the protests, though a recent Seton Hall Sports Poll found that 84% of Americans support the players’ right to protest.

NBA, NHL, pro soccer rise

As part of the survey, Gallup also asked about other sports. Football was one of only two sports to see a significant drop from five years ago; the other was Olympic sports, which fell 12 percentage points and isn’t likely to get much help from the 2018 Winter Games in PyeongChang, though it still has the biggest chunk of fans, at 63% of Americans. Pro baseball and college basketball saw drops of 2 percentage points each.

“Every other sport measured in the Oct. 10- Oct. 11 survey,” writes Gallup’s Jones, “did not change meaningfully from five years ago.”

But even though Jones labels the other swings not meaningful, it’s worth comparing them to football’s considerable drop. The comparisons paint a troubling picture for pro football.

Since 2012, the portion of Americans identifying as fans of pro basketball rose by 3 percentage points to 40%. Auto-racing fans and pro hockey fans each rose by 4 percentage points (to 32% and 28% of Americans, respectively). Pro soccer fans in America rose 5 percentage points, to 28%.

These numbers are encouraging for Nascar, the National Basketball Association, the National Hockey League, and pro soccer.

[For more on the business of the NFL, listen to our Sportsbook podcast. Episode 6 examines the future popularity of the league.]

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Daniel Roberts is the sports business writer at Yahoo Finance. Follow him on Twitter at @readDanwrite. Sportsbook is our sports business video and podcast series.

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