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This still image is taken from a television advertisement aired by John McCain’s presidential campaign in 2008 connecting Barack Obama with Bill Ayers. (Courtesy of Solomon Messing of the Pew Research Center/John McCain for President)

*A new study shows that negative ads targeting President Obama in 2008 depicted him with darkened skin, and that these images would have appealed to some viewers’ racial biases, reports the Washington Post.

The finding reinforces charges that some Republican politicians seek to win votes by implying support for racist views and ethnic hierarchies, without having to come out and say it.

The tactic is referred to as “dog-whistle politics” — just as only dogs can hear a dog whistle, only prejudiced voters are affected by the racist connotations of a politician’s message, according to the theory.

That debate has been prominent in the 2016 campaign, primarily targeting Donald Trump, but it has existed in almost every recent presidential election, notes WaPo: “To hear their opponents tell it, when Republican politicians say they oppose a generous welfare system, they really mean black beneficiaries are lazy. If they endorse strict immigration enforcement, they really mean that Latinos are criminals, critics say.”

A study published online this month in Public Opinion Quarterly specifically cites Sen. John McCain’s 2008 campaign, which — intentionally or not — has aired advertisements that exacerbate viewers’ racial biases:

Analyzing 126 advertisements from the presidential campaign in 2008, the authors first digitally measured the darkness of the two nominees’ skin in each spot, then sorted the ads into categories based on themes. President Obama and his opponent, Sen. John McCain (R-Ariz.), looked very different in various advertisements depending on how the footage was edited and produced.

That was particularly the case in negative advertisements, in which each campaign manipulated the images of its opponent to shadow or wash out his face for dramatic effect.

Interestingly, though, when McCain’s campaign aired spots that connected Obama with alleged criminal activity by liberal groups, the producers almost always used images that made Obama’s skin appear very dark. You can watch one of those spots below.

Eighty-six percent of these ads contained an image of the president in which the his skin tone was in the darkest quartile of all ads studied.

Likewise, as the election approached, images of Obama in spots aired by McCain’s campaign became gradually darker.

Continue reading here.