Dr. Abdul El-Sayed holds a modest lead over Mike Rogers in part because of a strong advantage with younger voters, according to a New York Times/Siena poll.

© Shelby Tauber for The New York Times; Sarah Rice/Getty Images

The party’s nominees lead in Michigan and New Hampshire but the Republican incumbent is ahead in Maine, according to New York Times/Siena polls of the three battlegrounds.

© Jillian Vordick/The New York Times

The party’s nominees lead in Michigan and New Hampshire but the Republican incumbent is ahead in Maine, according to New York Times/Siena polls of the three battlegrounds.