A warning that a far-left political movement is gaining real ground in America, framed as a serious threat by the conservative side.

• The alarm centers on New York City electing a young, hard-left candidate seen as radical and pro-jihadist.
• The claim is that many Americans back this movement partly out of anger at Trump.
• The bigger point: this shift is being underestimated and should be taken more seriously.

Outlook: Expect this to become a louder fight as the political left and right clash over how far the movement can spread.