With the first Democratic debate slightly more than two weeks away, Clinton is batting away suggestions from antsy supporters that she take on Sanders and his unabashedly far-left views. She insists, people who have spoken to her recently said, that time will prove her right.

But her reticence is sowing unease among some backers, who argue she should confront the Sanders threat more directly. One backer, who asked not to be named in order to speak more freely, said Clinton risks looking overconfident or oblivious to the challenge Sanders poses.

“Bernie Sanders is not Barack Obama, for many reasons,” the backer said. “Still, a lot of us remember what it looked like last time,” a reference to Clinton’s 2008 run for the nomination.