Vermont Sen. Bernie Sanders, Massachusetts Sen. Elizabeth Warren, former South Bend, Indiana, Mayor Pete Buttigieg and former Vice President Joe Biden are in a tight battle in  Iowa, three weeks ahead of the state’s caucuses. All are within 5 points of each other in the latest CNN/Des Moines Register/Mediacom poll. 
    
    
            Sanders clocks in at 20%. Warren has 17%. Buttigieg slides in with 16%. Biden rounds them out with 15%. Results for the full sample of likely caucusgoers have a margin of sampling error of plus or minus 3.7 percentage points.
    
    
            No other candidate reaches the double-digits. 
    
    
            The big story here is that Sanders is up from 15% in our November poll and 11% in our September poll. It’s the first time Sanders has been in the 20s since last March. 
    
    
            On the other end, Buttigieg has seen his fortunes decline. He’s dropped 9 points since being the clear leader in our last Iowa poll, when he was at 25%. 
    
    
            Interestingly, Warren seems to be holding on to most of her first choice support. Despite lots of noise of her losing ground, her 17% here is quite similar to her 16% in November. 
    
    
            Biden’s 15%, despite visiting the state a lot, is the same as it was in November. 
    
    
            Minnesota Sen. Amy Klobuchar at 6% and entrepreneur Andrew Yang at 5% are the only other candidates at or above 5%.