As he formally announces his run for the presidency, it is nothing short of astonishing that Sen. Bernie Sanders, the Vermont socialist who will be 75 years old on Inauguration Day 2017, has emerged as Hillary Clinton's leading opponent in the race for the Democratic nomination. But that is what has happened.

A new Iowa survey by the Democratic polling firm PPP finds Clinton with an overwhelming lead over the Democratic pack — no news there. But PPP also found that, while the former secretary of state is the choice of 62 percent of Democrats surveyed, Sanders is now in double digits, with 14 percent saying they support him. (Martin O'Malley is at 6 percent, Jim Webb at 3 percent, and Lincoln Chafee at two percent, while 13 percent say they are not sure who they support.)

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Given the peculiar character of the Democratic race, just being in double digits qualifies a candidate as a legitimate opponent of Clinton. And PPP numbers also put Sanders in double digits in New Hampshire. "We've now found that in both Iowa and New Hampshire, Sanders is the second choice," says PPP director Tom Jensen. "If there really is a desire on the far left for anyone else — now that they're not going to get Warren — Sanders may be their guy."

What appears to have happened is that Sanders has become a stand-in for Warren among those Democrats who wanted the Massachusetts senator to run and are disappointed that she has declined. They have now transferred their support to the next-best candidate to represent their point of view, and that is Sanders.

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One indication of that is in the PPP data from Iowa Democrats who describe themselves as "very liberal." Among them, Clinton's lead over Sanders is 55 percent to 29 percent — still a big lead at 26 points, but far less than Clinton's 48-point lead among Democrats overall.

Yes, Clinton is far, far ahead. But in the big picture, the PPP results show that despite her lead, 38 percent of Democrats in the key early state of Iowa either do not want Clinton as their nominee or are not sure who they support. No, that's not enough to win. But for her would-be opponents, it's a start.

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