Bernie Sanders in 2015 has caught up to Obama's polling numbers in 2007. Image comparing polls from both years.
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On August 11, Harry Enten of FiveThirtyEight wrote that "The Bernie Sanders Surge Appears To Be Over." On that day Bernie Sanders had an average of 19.4% according to RCP's poll average. On August 25, 14 days after that article, Bernie Sanders has an average of 27.7% on RCP's poll average.
Washington Post
So far so good for the upstart Sanders campaign. According to Sanders, Phase I of his campaign was a national introduction as he competes with a candidate who has universal name recognition.
Longtime Democratic strategist Tad Devine, ... said Sanders has the potential to assemble “not necessarily the same coalition, but the same kind of coalition” as Obama did in 2008. Sanders’s huge campaign rallies have been heavily attended by younger voters, and during his long political career in Vermont, he has demonstrated an appeal to lower-income voters from both parties.
Phase II of Sanders campaign will be a challenge (not to say that attracting 20,000+ to rallies was not!) but it's a different challenge of reaching out and should be interesting.
Campaign manager Jeff Weaver said the senator will continue to hold rallies but “phase two will be a more focused effort to reach out to undecided voters” in early nominating states. The campaign is spending heavily in Iowa, New Hampshire, Nevada and South Carolina — all of which have contests in February — and starting to evaluate strategies for a dozen states that have primaries or caucuses on March 1.
[...]
Another focus of “phase two,” according to Sanders and his aides, will be a series of detailed position papers and policy speeches that go well beyond his hour-long stump speech.
Sanders said he plans a major address on Wall Street reforms and to add more specifics to many of his ideas, including revamping the tax system. He has pledged to reverse the growing income inequality in the country and has laid out a set of costly priorities — including free tuition at public colleges and universities, a massive infrastructure program and a large youth jobs program — much of which would be paid for by taxing businesses and the wealthy.
“It’s easy to say we’re going to make the corporations and wealthy pay their fair share,” Sanders said. “What does that mean, exactly?”