Slipping in polls under an onslaught of attacks, Republican presidential contender Newt Gingrich promises to wage a sharper and more aggressive campaign in the final two weeks before Iowa kicks off the party's nominating race. Gingrich says he will be quicker to respond to attacks and more agile in getting his message across to voters who may have lost faith in him after rivals launched a withering barrage of criticism of his past as a Washington insider. A 44-stop bus tour in the run-up to the January 3 Iowa caucus, daily calls with supporters to respond to new criticisms and...