Bernie Sanders's momentum is running smack into demographic reality.

His base is white and male. Frontrunner Hillary Clinton is still crushing him with both whites and men. And Democratic elected officials say Sanders hasn't laid the groundwork to cut into her prohibitive leads with African Americans and Hispanics.

"The message that Bernie brings forward in normal circumstances would find pockets of support," said Rep. Chaka Fattah, a black Philadelphia Democrat who backed Barack Obama over Clinton in the 2008 Democratic presidential primary. "The challenge that he has is the overwhelming level of support that Hillary has. ... The case is closed."

A Washington Post poll released earlier this month showed Clinton beating Sanders 62 percent to 8 percent among women; 62 percent to 14 percent among men; 72 percent to 5 percent among nonwhites; 56 percent to 14 percent among whites; and 63 percent to 17 percent among liberals.

"We don't know yet who the Bernie Sanders voter is going to be"

And an NBC/Wall Street Journal poll released this week showed Clinton leading Sanders 75 percent to 15 percent overall. There is a sliver lining for Sanders: He appears to be consolidating the anti-Clinton vote, as former Sen. Jim Webb of Virginia and former Maryland Gov. Martin O'Malley barely register in national surveys.

A fine start

Sanders's path to the Democratic nomination is as narrow as a fiber optic wire, twisted like the plot of a Gillian Flynn novel, and guarded by Clinton, a candidate who has a primary lead reminiscent of Al Gore's over Bill Bradley in 2000. Even if she were to bow out, it seems likely that Democratic leaders would look for another standard-bearer.

Still, senior Sanders adviser Tad Devine, an expert on the party's nominating rules who worked for Jimmy Carter, Al Gore, and John Kerry, said the Vermont senator already has taken his first major step toward viability.

"It begins with establishing Bernie as the strongest alternative to the frontrunner," Devine said in an interview with Vox last week. "I think that break from the pack has already begun."

A tall order

The rest of the plan, according to Devine, looks something like this:

Raise $40 million to $50 million, mostly from small-dollar donors, for the first four primary contests — Iowa, New Hampshire, South Carolina, and Nevada — and to get on the ballot in the remaining states. Spread Sanders's message — centered on income inequality, climate change, and campaign finance reform — which the campaign believes will resonate in Iowa because, like Vermont, it is rural, dotted with small towns, averse to candidates who talk like politicians, and overwhelmingly white. New Hampshire is smaller and a little wealthier in terms of median household income, but not terribly unlike Iowa. Do well enough in Iowa and New Hampshire that those donors will give again and replenish the campaign's coffers. The trick for both candidates: defining success. Some of the new money would be used for more sophisticated voter identification.

Use the new money to tell Sanders's story in other parts of the country, relying on his work as a civil rights activist and his background as the son of a Polish immigrant father to appeal to black and Hispanic voters. Persuade Democratic superdelegates — the party leaders who have automatic votes at the convention — that he is the best candidate to represent the party because his coalition includes traditional Democrats and white working-class voters who weren't voting or were voting Republican.

"We don't know yet who the Bernie Sanders voter is going to be," Devine said. "I think Bernie has the potential to expand beyond white, working-class voters and liberal voters as he tells his story."

The Hillary Clinton voter

Maybe, if everything went right, Sanders could make a serious dent in the Clinton machine in Iowa and New Hampshire, but the states right after that on the primary calendar — and many of the big states that follow — are heavily influenced by minorities.

In the handful of polls taken in South Carolina and Nevada this year, Clinton snags between 50 percent and 60 percent of the Democratic electorate, and no one else is within 30 points of her.

Democrats say that has a lot to do with the relationships Clinton has developed with Democratic activists and voters over the years — ties that Sanders will have trouble creating in the months before voters go to caucuses and polling stations.

"I do know that Secretary Clinton has a long history, and that will be rewarded, I'm sure," said Rep. Sheila Jackson Lee, a Texas Democrat who backed Clinton in 2008.

Numbers are on Clinton's side

It's not just that Sanders would have to convince black and Hispanic voters — and women of all races — that he's a good candidate. He's in the position of convincing many of them that he should supplant Clinton as their favorite.

They know her, and they're with her. To win, he would have to get them to leave her.

Clinton beat Obama with Hispanics by a margin of nearly 2 to 1 in their 2008 primary contest, according to data compiled by Pew, and her poll numbers show that black voters aren't holding the 2008 campaign against her. That's probably the result of Clinton working for Obama for four years after she lost.

Members of the Congressional Black Caucus say she's not likely to lose much ground to Sanders because she has deeper ties to African-American voters. And while many of them say Sanders is talking about important issues of inequality on the stump, they're gravitating toward Clinton.

"He has a role to play in bringing the issues forward that he doesn't think Mrs. Clinton will raise," said Rep. William Lacy Clay (D-MO). "I don't have any comment on his viability."

Clay endorsed Clinton on Tuesday.