Democratic presidential hopefuls: from left, Elizabeth Warren, Beto O'Rourke, Amy Klobuchar, Tulsi Gabbard, Jay Inslee and John Delaney during the debate in Miami. Bloomberg
Democratic presidential hopefuls: from left, Elizabeth Warren, Beto O'Rourke, Amy Klobuchar, Tulsi Gabbard, Jay Inslee and John Delaney during the debate in Miami. Bloomberg

2020 Democrats pledge return to Iran nuclear deal if they beat Donald Trump