Hillary Clinton of all people knows how political fortunes turn on a dime. But she must be puzzled nonetheless, and spooked, that over a six-month period when she made no big news whatsoever, her popularity took a double-digit tumble.

A poll released last week by NBC News and The Wall Street Journal charted the decline. It found that the percentage of Americans who view her favorably had dropped to 46 from 56. The percentage with unfavorable views had risen, less strikingly, to 33 from 29.

Here we go. The beginning of the end of her inevitability.

It’s about time, because the truth, more apparent with each day, is that she has serious problems as a potential 2016 presidential contender, and the premature cheerleading of Chuck Schumer and other Democrats won’t change that.

In the wake of the federal shutdown, in the midst of the Obamacare meltdown, voter disgust with business as usual is at the kind of peak that ensures more than the usual share of surprises in the next few elections. In one recent poll, 60 percent of Americans said that they’d like to see everyone in Congress, including their own representatives, replaced; in another, a similar majority hankered for a third party.