Senator Clinton's campaign is attacking Senator Obama over his position on guns . . . .The campaign has sent a mail piece to voters in Indiana that asks in large font, "Where does Barack Obama really stand on guns?" On the other side, it says: "Depends on who Barack Obama is talking to." The flier refers to . . . Mr. Obama saying he supported the Second Amendment in Idaho while also mentioning his oft-repeated statement from a San Francisco fund-raiser in which he said small-town Americans "bitter" over the economy "cling" to religion and guns. Both Democratic candidates favor gun control measures such as a ban on assault weapons and strengthening the federal background check system.