(Fortune) Saturday, President Donald Trump essentially called for a boycott of the NFL in response to players using the national anthem to protest police profiling of African-Americans.

Should Trump’s supporters respond to that call, the medium-term effects could be serious for the NFL. But the impact would be at least as bad, and much more immediate, for the broadcasters who pay to air games.

The anthem protests, which began with former 49ers quarterback Colin Kaepernick and have now spread throughout the league, already appear to be affecting NFL ratings. Last week, with the 2017 season barely started, ratings were down a stunning 15% year over year, according to the Hollywood Reporter – and that’s after an 8% slide last year.

Note: Read our discussion guidelines before commenting.