Opinion writer

Sen. Bernie Sanders (I-Vt.) speaks at a rally in Buffalo on Monday. (Brian Snyder/Reuters)

A familiar and self-defeating pattern among Democrats is emerging for a fourth consecutive presidential election cycle. It goes something like this: The favored establishment candidate faces a challenge from the left fueled by grass-roots fervor, money and media attention. Whether that challenger wins the nomination (Barack Obama in 2008) or loses (Howard Dean in 2004), there is always talk about how their following is the start of a movement that can no longer be ignored.

That is, until the presidential election is over. After that great day at the polls, despite all the heady talk of political revolution, those fired-up folks go home — and stay there for the next four years. The campaign of Sen. Bernie Sanders (I-Vt.) swears this time will be different. Sorry to be the skunk at the garden party, but it won’t.

“This campaign is changing people’s lives and changing everyone’s idea of what’s possible,” said Zack Exley of the Sanders campaign in the Nation magazine. “No matter what happens, people are going to keep fighting for the political revolution that Bernie helped all of us start. What’s more, these organizing teams, structures, and processes won’t have to be reinvented. They will live on. … This revolution is only just getting started.”

But as Doyle McManus of the Los Angeles Times points out in his column that alerted me to that Exley quote, there is a bit of historical deja vu and amnesia going on here. “We’ve heard that song before,” he writes. “In 2004, insurgent candidate Howard Dean tried to turn his campaign into a progressive movement, Democracy for America, with negligible results. In 2008, President Obama’s campaign staff tried to remake their grass-roots network into something called Organizing for America, but that effort failed completely.”

[A warning to warring Democrats in the Clinton-Sanders race]

Democrats always forget that political revolutions are not quadrennial affairs. They are as consistent as they are persistent in making the dreamed-of revolution a reality. That means showing up at the polls in off-election years, enthusiasm for which Democrats always fail to muster. And the consequences have been dire.

Take a look at the two charts below from Steve Phillips’s book “Brown Is the New White: How the demographic revolution has created a new American majority” Using data from the Office of the Clerk of the U.S. House of Representatives, the senior fellow at the Center for American Progress and co-founder of PowerPAC.org shows what happened after the revolutionary euphoria of the 2008 and 2012 presidential elections that elected and reelected Obama wore off.

(Courtesy of Steve Phillips)

In the 2008 election, 65 million Democrats cast ballots for House candidates. That number dropped to 39 million in the 2010 midterm elections. That 26-million-vote plummet helped flood the House of Representatives with tea party revolutionaries as the Republican Party took over the chamber with a gain of 63 seats.

(Courtesy of Steve Phillips)

In the 2008 elections, 33.6 million Democrats voted for Senate candidates. By the 2014 midterm elections, about 15 million fewer Democrats cast ballots. That 43 percent drop-off helped hand the Senate majority to the Republican Party. That was also the election that saw the GOP House majority increase to its largest since World War II.

“Even if their candidate falls short in the next few primaries, Sanders voters shouldn’t give up in despair,” McManus writes. “Their votes will still count, because the final score will matter — not only for this presidential campaign, but the next one.” That may be. But for the Sanders revolution to have any real impact after this presidential campaign, these voters have to make their power felt at the polls in 2018. The likelihood of this happening? Slim to none.

Follow Jonathan on Twitter: @Capehartj