“Undecided” is the leading 2020 presidential choice for Democratic primary and caucus voters, the latest indication that none of the estimated 25 candidates eyeing the race are moving to the front.

The latest Zogby Poll showed former Vice President Joe Biden falling back from his lead in May to a virtual tie with Vermont Sen. Bernie Sanders. In May, Biden led Sanders 26 percent to 18 percent. In June, it was 21 percent to 19 percent.