Why a GOP senator is the most vulnerable politician in the midterms

Sen. Ron Johnson (R-WI) is considered to be one of the most vulnerable Republicans facing reelection this year. CNN’s Manu Raju explains what he’s up against in his fight to stay in the Senate.Sen. Ron Johnson (R-WI) is considered to be one of the most vulnerable Republicans facing reelection this year. CNN’s Manu Raju explains what he’s up against in his fight to stay in the Senate.