Polls ahead of the Iowa caucuses suggest Sanders and Biden are in a tight race with Massachusetts Sen. Elizabeth Warren and former Mayor Pete Buttigieg of South Bend, Indiana. Sanders has confidently predicted victory in Iowa and in the Feb. 11 New Hampshire primary that follows, telling his supporters that the party establishment is “nervous” about his strength. His advisers argue that such momentum would dent Biden’s long-standing advantage in most national polls of Democratic voters.