The chart above is from the Monmouth University Poll -- done between November 7th and 11th of 966 registered Democrats and Independents in Iowa. The margin of error is 4.6 points.
It shows that Pete Buttigieg has climbed into the lead in Iowa with 22% support. But Biden (19%) and Warren (18%) are both within the poll's margin of error, so it could be considered a three-way tie. Sanders is in fourth at 13%, and no one else tops 5%.
This is indicative of the excellent organization Buttigieg has in Iowa. But he is not as organized on the national level. He is counting on a good finish in Iowa to boost him nationally.
The chart below is also from the Monmouth University Poll. It was done between October 30th and November 3rd of a national sample of 345 registered Democrats/Leaners, and has a 5.3 point margin of error. Note that Buttigieg is not in double-digits nationally, and is running far behind Biden, Warren, and Sanders.