is race between clinton and sanders even tighter? plus, donald trump threatening to boycott thursday's debate. is he going to walk? michael bloomberg for president. could the race come down to the battle of billionaires? let's go "outfront." >>> good evening. i'm erin burnett. we begin with breaking news. bernie sanders closing in on hillary clinton. this is a new national poll we are just releasing here on cnn. it comes as sanders and clinton are in final preparations for the cnn presidential town hall. you can see live pictures of the stage. this will be sanders and clinton's last chance to state their case to voters before the iowa caucuses. clinton's once lead narrowing under the sanders' surge. clinton leading sanders and she is leading still 52% to 38%.