Mayor Bloomberg’s $12 million ad blitz backing gun control causes headaches for Democrats in gun-friendly territory – Mayor Bloomberg’s $12 million ad blitz to drum up Senate support for background checks on all gun purchases could backfire, Senate strategists said Monday.  Bloomberg said Sunday that his group, Mayors Against Illegal Guns, will spend a fortune over the next two weeks on television ads aimed at pressuring wavering senators to support background check legislation. Voting is expected to start around April 9.  The ads are running in 13 states while senators are home for a two-week Easter recess.