EL RENO, Okla. — President Obama, who in recent weeks has shed any reticence to talk about racism and discrimination in American life, suggested inside the walls of a federal prison in Oklahoma on Thursday that under different circumstances, he could have been there as an inmate rather than as president. “That’s what strikes me — there but for the grace of God,” the president said, standing in an empty cellblock with polished concrete floors and gray-and-white walls. Minutes after he had finished meeting with six nonviolent drug offenders in El Reno federal prison, a medium-security facility, Obama said his...