The charts above are from the Des Moines Register & CNN Iowa Poll -- done between March 3rd and 6th of 401 likely Democratic caucus attendees in Iowa, with a 4.9 point margin of error.
Joe Biden has not yet declared his candidacy, but he leads in Iowa. He has a two point lead over Bernie Sanders, an 18 point lead over Elizabeth Warren, and a 19 point lead over Kamala Harris.
When you add in the second choices of caucus attendees, Biden's lead over Sanders grows to 9 points. The lead over Warren grows to 25 points, and the lead over Harris grows to 28 points.
It's still very early, and these numbers are sure to change, but I found them interesting. Will Biden's lead grow when he declares his candidacy, or not?