Via The Hill:

Hillary Clinton’s campaign is “worried” about Bernie Sanders, who a top Clinton aide described as a “serious force” in the 20116 battle.

“We are worried about him, sure. He will be a serious force for the campaign and I don’t think that will diminish,” Clinton communications director Jennifer Palmieri said Monday in an interview with MSNBC’s “Morning Joe.”

“It’s to be expected that Sanders would do well in a Democratic primary and he’s going to do well in Iowa in the Democratic caucus.”
Sanders, an Independent senator from Vermont, has emerged as Clinton’s main foil in the Democratic primary.