By WILLIAM SCHNEIDER — Politico.com

The Massachusetts message to Democrats is, “Be afraid. Be very afraid.” Because a full-scale populist revolt is breaking out in the country. Again.

Sen.-elect Scott Brown said on Tuesday night, “[Democrats] will be challenged again and again across this country. When there’s trouble in Massachusetts, there’s trouble everywhere. And now they know it.”

A populist revolt is “us” versus “them.” “Us” is “we the people.” “Them” is the governing class. Right now, the governing class is mostly Democratic. It certainly is in Massachusetts, where every member of Congress, every statewide elected official and nearly 90 percent of state legislators are Democrats.

Why is this happening? For two reasons. One is the same reason it happened in the late 1970s and again in the early 1990s: the economy, stupid.

When joblessness goes up and the government doesn’t seem to be able to do anything about it — or worse, when the government spends a lot of money and it doesn’t seem to be doing much good — voters get mad. They take out their rage on political insiders. Throw the bums out! Cut their allowance! Limit their terms!

That’s what angry voters did during the “malaise crisis” of the late 1970s. It took the form of a tax revolt, starting in California with Proposition 13 in 1978. Jimmy Carter became a one-term president. In 1978, Massachusetts Gov. Michael Dukakis was defeated for renomination by a conservative Democrat. Off with their heads!

It happened again in the recession of the early 1990s. Then it took a form of a term limits movement, which spread all over the country (including Massachusetts). George H.W. Bush became a one-term president. Pat Buchanan’s “pitchfork brigades” raged across the land. Ross Perot started a voter uprising.

In 1994, angry white men rose up and overthrew the Democratic Congress after 40 years in power. Up against the wall!

Then it was Rush Limbaugh, Newt Gingrich and the Contract with America. Now it’s Glenn Beck, Sarah Palin and the Tea Party movement.

The second thing driving the revolt is anger at Congress. It is always dangerous for Congress to act in defiance of public opinion.

The Republican Congress defied public opinion by impeaching President Bill Clinton. As a result, Democrats picked up seats in the 1998 midterm and Speaker Gingrich was forced to resign.

At the end of 2008, Congress gave Wall Street a bailout. The President – Bush not Obama — signed it into law. That produced the Tea Party movement.

Now Congress is on the verge of passing health care reform — in defiance of public opinion. Doesn’t the public want health care reform? They do — in principle. But polls show the public doesn’t like these particular bills. Too expensive. Too disruptive. Too many insider deals.

Most Americans say they’re satisfied with their health care and their health insurance. And they want everyone to have it. But they’re anxious about being forced to change what they have and like. Particularly seniors. When President Obama talks about “Medicare savings,” seniors hear “Medicare cuts.”

The Massachusetts campaign was widely seen as a referendum on health care reform — in a state that already has it. In fact, Scott Brown voted for it as a Massachusetts state senator. Nonetheless, Brown has pledged to cast the 41st vote that would kill the bill in the U.S. Senate.

What happens now?

Some congressional Democrats are talking about pressuring the House of Representatives to pass the Senate bill as is, so the president can sign something before next week’s State of the Union speech. The Senate bill is “clearly better than nothing,” House Democratic Leader Steny Hoyer (Md.) said on Tuesday.

That won’t be easy. The House passed its bill in November with only five votes to spare. Terrified House Democrats from swing districts are more likely to move against the bill than for it. If this is what happens in Massachusetts, they tremble to think what could happen to them in Missouri or Colorado or Tennessee.

Congressional Democrats are caught between a rock and a hard place.

The rock: If they kill health care reform, they’re courting the same disaster that befell the Democratic Congress in 1994 after it pulled the plug on the Clinton plan.

The hard place: If the House passes the Senate bill, Democrats could face an enraged electorate.

Can Obama get them out of this? He’s hoping to with a populist tactic of his own — economic populism. It’s one of the oldest weapons in the Democratic arsenal. The president signaled that strategy on Sunday, when he condemned “an era of greed and irresponsibility that sowed the seeds of its own demise.”

The question is: Will voters blame the banks and the insurance companies and the oil companies for corrupting government? Or will they blame government?

Obama campaigned for Democrat Martha Coakley in Massachusetts. Democrats all over the country are likely to conclude that Obama can’t offer them political cover. Think they’re going to stick their necks out on other difficult measures now, like a cap-and-trade energy bill or immigration reform?

Obama will make the case that Democrats must to pass things or die. Massachusetts said, you pass things we don’t want and you die.

Is there a solution to this dilemma? Sure. It’s called economic recovery. Congress has to pass whatever it can to create job growth. That’s what saved President Reagan in the 1980s. And President Clinton in the 1990s.

There’s only one way to stop a populist revolt: prosperity.

William Schneider is the Hirst Professor of Public Policy at George Mason University and Resident Scholar at Third Way, a public policy research institute.