Phil Griffin, the president of MSNBC, called me on Monday. He’d read my first piece on the killing of Trayvon Martin, the one where I list the “don’ts” that I was taught as a 16-year-old in Newark, N.J. He wanted to put pictures behind my “powerful” words and have the story air on “Politics Nation,” the 6 p.m. show anchored by Rev. Al Sharpton. Yesterday, for the first time in more than 25 years, I walked along Meeker Ave. with Sharpton to talk about Trayvon and what I was taught in the hopes that I would not arouse undue suspicion and meet a similar fate.