As the Democratic field for president thins out, most supporters of the dropouts will pick another candidate. That prospect raises the question of whether these newly available voters will flock to the front-runners or boost the chances of one of the also-rans. To gain insight into this question, the latest YouGov polls asked respondents likely to vote in Democratic primaries to name both their first and second choices for the nomination. In the most recent survey, Joe Biden leads on first-choice ballots, followed by Elizabeth Warren, Bernie Sanders, Pete Buttigieg and Kamala Harris. So what happens to the horse race when we add in the second choices of potential voters?