When Bernie Sanders announced he would be running for president late in the spring of 2015, many observers didn't take him seriously, making analogies to failed perennial candidates like Ron Paul, who had a fervent base but did not get traction in the election. The problem with these early predictions is that it quickly became clear they were underestimating the Vermont senator's campaign.

In three key areas, Sanders is actually exceeding the insurgent campaign Barack Obama ran in 2007 and 2008.

Record-Breaking Crowds

Over the summer, it became clear that Sanders was drawing some of the largest crowds in Democratic primary history, with tens of thousands pouring out into cities to see the senator.

Up until this point in 2007, the largest rally Obama had held was in New York City, our nation's most populated location, which brought out 24,000 people. Sanders has exceeded that in numerous locations that are actually much smaller in population: Boston, Portland and Los Angeles. Earlier this month, Sanders set a record for the largest Democratic primary rally in Boston's recorded history.

Sanders' campaign is working hard to translate these crowds into volunteers. In late July, his campaign mobilized over 100,000 people for community meetings to support his bid; today, his campaign has developed a map that shows all of the organizing events currently planned:

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At the end of September, the Sanders campaign announced it had hit one million donations — faster than any presidential campaign in history. This was a target the Obama campaign did not hit until February 2008 during his challenge to Hillary Clinton. Perhaps even more remarkable is that this milestone was achieved with an average contribution of $24.86; although the Obama campaign was quick to boast of its sizable number of small donors, less than half of his money, 47 percent, ended up coming from small donors.

Polling Stronger Than Obama

Obama managed an upset of frontrunner Hillary Clinton that few believed possible. But at that point in his initial campaign, he was polling well behind her. Real Clear Politics has a chart showing polling averages among major pollsters for that primary. In early October, Obama was at 22.6 percent to Hillary Clinton's 48.2 percent.

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There is also a chart for this primary. Sanders is at 25.4 percent to 42 percent for Hillary Clinton, meaning that the gap is around 17 points, when it was 26 points between Obama and Hillary at this time.

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None of this is to say Sanders will necessarily defeat Clinton. Much of that depends on his ability to defeat her in early primary and caucus states, which would give him the momentum for Super Tuesday and the rest of the nation's primary elections. The Obama campaign's strong ground teams in Iowa, New Hampshire and South Carolina gave him the momentum to increase turnout and defeat the frontrunner who was trouncing him just a few months prior. For Sanders, these early elections will be the deciding days, to see if he can continue on a viable path to the White House.