Some Buffalo Bills players take a knee during the national anthem before an NFL game with the Atlanta Falcons in Atlanta. (AP Photo/John Bazemore)

Over the past month, President Trump has repeatedly stoked the controversy about protests during the national anthem at professional sporting events. He resumed that critique after Sunday’s National Football League games:

But have Trump’s objections to these protests pulled Americans to his side? No. In fact, a new poll suggests it’s exactly the opposite.

The poll, conducted Oct. 15-17 by HBO Real Sports and Marist College, found that an increasing number of Americans believe that professional sports leagues should not require athletes to stand during the national anthem. In this October poll, 51 percent said that standing should not be required. In a September 2016 poll by HBO and Marist, only 43 percent said this.

The shift is particularly sharp among Democrats, whose opposition to requiring athletes to stand has increased by 13 points. Meanwhile, Republican opposition has declined. Self-described independents look more like Democrats: Their opposition to requiring athletes to stand has increased from 47 percent to 54 percent.

If you know your political science, this is an entirely predictable finding. When presidents take visible positions on issues, it naturally polarizes public opinion. As citizens, we routinely take cues from political leaders in our party — or react against leaders in the opposite party.

Repeatedly during Trump’s presidential campaign and presidency, the net effect of this polarization has been to move overall opinion against his views. During the campaign, for example, Americans’ opinions of Muslims became more favorable. Support for a border wall with Mexico decreased.

Indeed, in this new HBO-Marist poll, 68 percent of respondents, and 41 percent of Republicans, said that Trump did the “wrong thing” in criticizing the athletes who have knelt during the anthem. Only 41 percent said the athletes themselves were doing the wrong thing.

This is one of the hardest lessons for all presidents to learn. There is always a temptation to use the bully pulpit. But it’s not clear that it helps.