(Andrew Harnik / Associated Press)

Sens. Bernie Sanders and Elizabeth Warren will both campaign this weekend in Ohio for Hillary Clinton, underscoring the need for both presidential nominees to turn out core supporters in the tightening election.

Sanders, the democratic socialist from Vermont who ran a tough campaign against Clinton, and Warren, the Massachusetts Democrat viewed as the leader of her party's progressive wing, have both given Clinton a qualified embrace. The two have made it clear they will work hard to defeat Donald Trump, but will continue to hold Clinton accountable from the left.

Ohio, with large numbers of white working-class voters who were drawn to Trump during the GOP primary, is one of a small group of crucial swing states. Polls there have tightened to a dead heat, with more recent surveys showing an edge for Trump.