Vermont Sen. Bernie Sanders is stirring up a lot of enthusiasm among liberal activists as he campaigns for the 2016 Democratic presidential nomination. But will he be able to convert that energy into a viable national campaign that can take on Hillary Clinton, the party's dominant frontrunner?
There's certainly no shortage of excitement surrounding Sanders' bid. The senator has drawn crowds in excess of 10,000 at multiple rallies around the country. And on Wednesday, more than 100,000 people RSVPed to attend a gathering of Sanders supporters, watching as the candidate's speech in a Washington, D.C. apartment was broadcast live to thousands of other parties nationwide.
It was an impressive turnout, and Sanders' campaign suggested it came together without much heavy lifting on their part.
"100,000 people in 50 states is a demonstration of how much we can build, and how inexpensively we can build it," Sanders' chief strategist, Tad Devine, told CBS News. "We didn't spend millions of dollars to pull that event off on Wednesday."
According to public polling data, Sanders has emerged from the pack as the strongest Democratic rival to Clinton. His campaign is eager to build on that momentum, but they admit they have their work cut out for them.
"I think we were initially surprised by how much interest and excitement there was," Devine said. "Once these big crowds started appearing, I don't think we were as surprised as we were before...We're obviously very pleased about it, [but] this is really just the beginning. In order for this to succeed, we're going to have to make it much bigger. Now the test is can we put together a ground organization in early states and get ballot access everywhere."
Not everyone is convinced Team Sanders can make that happen, though. Clinton still has a lot of assets on her side, including more money, a more robust organization, and more endorsements from elected officials. That foundation is tough to discount. There are also signs Sanders may have trouble wooing core Democratic constituencies like Black and Latino voters, who are drawn to his populist message on income inequality but need to hear more about his stance on institutional racism, police reform, immigration reform, and other issues.
There would also be the uphill battle to convince Democratic Party officials that nominating a self-described "independent socialist" wouldn't doom the party in the 2016 general election.
With that in mind, here are five reasons Clinton's campaign isn't sweating the "Sanders surge" - at least not yet.