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Another report that Trayvon was serving a school suspension because traces of marijuana were found in his book bag was labeled by Mr. Sharpton “not violent and not material to this.”

MSNBC said that one of Mr. Zimmerman’s defenders was on “Hardball” Monday, which airs before Mr. Sharpton’s show, indicating that Mr. Sharpton’s advocacy hasn’t affected the network’s ability to seek the other side of the story.

It’s too early to tell whether Mr. Sharpton’s dual roles will pay off in the ratings for MSNBC. His show averaged 776,000 viewers during the first three months of the year, well behind the 1.8 million who watch Bret Baier on Fox News Channel during that hour but above the 459,000 who tune in to John King on CNN, the Nielsen company said.

In recent years, some cable news anchors have gotten in trouble for mixing advocacy and activism. Fox News Channel two years ago barred opinionated prime-time host Sean Hannity from speaking at a tea party rally and fundraiser in Cincinnati and also featuring the event on his show, ordering him back to New York.

In November 2010, MSNBC suspended prime-time host Keith Olbermann for two nights for donating money to political campaigns. Mr. Olbermann left the network two months later. Mr. Griffin noted that Mr. Sharpton would also be barred from making political donations at MSNBC, and said the situation was different from the Martin case because the donation was concealed from MSNBC executives and viewers. Mr. Sharpton, he said, is open about his activities.

Just because Mr. Sharpton has been allowed his dual roles doesn’t mean that MSNBC’s Lawrence O’Donnell or Ed Schultz would be allowed to speak at political rallies, Mr. Griffin said.

“It’s a different world we are sort of trailblazing,” he said. “The critical part of it is you have to be upfront about it. You can’t hide anything.”

Ms. McBride said she does not view Mr. Sharpton as a journalist and doubts that many viewers do. The reason MSNBC puts Mr. Sharpton on the air is because it wants to reach an audience that is interested in things that he is, she said.

“I’m not saying this is without problems,” she said. “I think it’s very confusing. But it’s certainly the way we are moving in the journalism industry.”