Bernie Sanders has gotten further in the 2016 presidential than a 74-year old self-professed Democratic Socialist might reasonably expect. He's ahead of Hillary Clinton in New Hampshire, nearly bested her in fundraising over the past three months and is drawing crowds in the thousands everywhere he goes.

Despite all of those successes, Sanders still faces one major problem in this campaign: Huge majorities of Democrats don't think he can win.

The new Washington Post-ABC News poll tells the story. Asked who they thought would win -- no matter which candidate they supported -- only one in 10 Democrats (11 percent) named Sanders. By contrast, 65 percent chose Clinton and 14 percent opted for Joe Biden -- even though he's not actually running just yet. Isolate just self-described liberals -- who comprise Sanders's base -- in that same poll and the result doesn't change much; 67 percent name Clinton as the party's most likely nominee while 13 percent chose Sanders and 12 percent Biden.

Take Biden out of the equation and the numbers are even more stark;  Nearly three in four (73 percent) of Democrats and Democratic-leaning independents say that Clinton will be their nominee while just 21 percent choose Sanders.

Those numbers should be sobering for people who see Sanders as a genuine threat to Clinton.  He's not. At least not yet.

How does Sanders solve that problem? It's not clear that he can -- at least in the near term.  The best way to convince people that you can win is to, well, actually win something; New Hampshire looks like Sanders's best chance to do that but that's not until February. And  some of his prospects in New Hampshire (and Iowa) are dependent on convincing people that voting for him is something more than a protest ballot.

While Sanders will always have a committed core of supporters who will be for him no matter what, that's not nearly enough people to make him viable against Clinton or against Clinton and Biden. People outside of that core tend not to like throwing their their vote away or to find themselves on the losing side of things. At the moment, that's what Sanders looks like.  He'll need to find a way to change that perception over the next few months if he wants to have a real chance of competing for the nomination.