… The cause of Mr. Biden’s weakness in Iowa is fairly obvious: His national edge is mainly attributable to a wide advantage among black voters, and relatively speaking, there aren’t many black voters in Iowa. African-Americans represented a mere 4 percent of Hillary Clinton’s 2016 supporters in Iowa, according to Upshot estimates. (They represented 22 percent of her support nationwide.) The latest Quinnipiac poll gives Mr. Biden a mere three-point lead nationally among white voters, who could make up around 90 percent of the caucus vote in Iowa.
The state’s Democratic voters are also relatively young, and caucuses tend to favor ideologically consistent, progressive candidates with highly engaged grass-roots support. CONT.
Nate Cohn, New York Times