California Democratic Sen. Barbara Boxer today urged anti-war activist Cindy Sheehan not to challenge the state's senior senator, Dianne Feinstein, in the June Democratic primary. Sheehan, whose son was killed in Iraq, has been actively considering a campaign after criticizing Feinstein for refusing to call for an immediate withdrawal of U.S. troops from Iraq. But Boxer, a liberal former Marin County supervisor who strongly opposed the war in Iraq, said Sheehan might actually hurt her anti-war cause by jumping into the race against her fellow Democrat who is entering her 14th year in the Senate. "I don't think having her...