It was bad news for Bernie Sanders that he lost in Nevada Saturday. But there may be a bigger crisis embedded in the loss: It suggested he isn't delivering on a key ingredient needed for his "political revolution."

On Saturday, about 80,000 voters participated in Nevada's caucus — roughly two-thirds of the total that came out in 2008.

Sanders's reason for running, as he describes it, is to upend how money and special interests shape American politics by empowering voters. This means bringing out an unprecedented number of people on Election Day.

So as bad as it was to lose Nevada on Saturday night, the tepid voter turnout in itself is almost a more significant problem for him.

Why low turnout is such a problem for Sanders's candidacy

Throughout the course of his campaign, Sanders has promised to transform American government by bringing "millions and millions" of new voters to the ballot box.

This is in contrast to the incrementalism of Clinton's campaign, which recognizes the confines of a bitterly divided American electorate and offers to fight for whatever gains are available.

Sanders rejects the limits of this system. His "political revolution" is based on the idea that Democrats could win big with a message that gets a massive number of new lower- and middle-income voters continually engaged in the political process.

It's an inspiring vision. But there is little sign that it's actually happening.

Low turnout in Nevada wasn't an outlier. New Hampshire saw 10 percent fewer voters in 2016 than it did eight years ago. In Iowa, turnout was also down — from 287,000 in 2008 to 171,000 this year. (By contrast, voter numbers are exploding on the Republican side, with records for GOP turnout being crushed in Iowa, New Hampshire, and, from the early results, South Carolina.)

Sanders needs this to change, and quickly, to validate one of his key arguments against Clinton.

As Vox's Ezra Klein has written, Sanders thinks "the core failure" of Obama's presidency is its failure to convert voter enthusiasm in 2008 into a durable, mobilized organizing force beyond the election. Sanders vows to rectify this mistake by maintaining the energy from the campaign for subsequent fights against the corporate interests and in congressional and state elections.

The relatively low voter turnout in the Democratic primary so far makes this more sweeping plan seem laughably implausible. Three states have voted, we've had countless debates and town halls, and there's been wall-to-wall media coverage for weeks. Sanders has drawn close to Clinton in the polls, and there are real stakes in a closely divided race.

And yet ... we have little evidence that Sanders has actually activated a new force in electoral politics. If he can't match the excitement generated by Obama on the campaign trail, how can he promise to exceed it once in office?