We already knew that Republicans were concerned about how campaign attacks during this presidential election cycle might backfire if perceived as racist or sexist. In a memo obtained by the Politico's Jonathan Martin, Rick Davis -- John McCain's campaign manager -- drives that point home to some of his campaign's top allies.

"Overheated rhetoric and personal attacks on our opponents distract from the big differences between John McCain’s vision for the future of our nation and the Democrats," Davis wrote. McCain "has held himself to the highest standards and he will continue to run a respectful campaign based on the issues ... We expect that all supporters, surrogates and staff will hold themselves to similarly high standards when they are representing the campaign."

Though Davis' memo does not mention Barack Obama by name, Martin says the missive was prompted by recent attacks by some Republicans who used Obama's middle name to smear him, falsely, as a Muslim. Some people in the McCain campaign, Martin reports, have been complaining privately about these attacks. "McCain officials have privately expressed irritation at the trend as it forces the candidate off message and into an increasingly-familiar apologize-and-denounce pattern. But they said they were limited from taking more proactive steps to curb the Muslim smear before they were designated the presumptive nominee," Martin says.