The Democrats are having their own tea party problem. With the "progressive" movement hawking a more populist liberal agenda, mainstream Democrats are going to have to start looking over their left shoulders, just as traditional Republicans now fear challenges from the right.
Remarkably, this could make the current dysfunctional, hyper-partisan climate in Washington worse. Or it could create a radical realignment of American politics for the better.
Let's start with the Democratic family feud. Senior executives from Third Way, a think tank promoting moderate, left of center policies, decried the economic populism of Democrats like Massachusetts Sen. Elizabeth Warren and New York Mayor-elect Bill de Blasio as a "dead end" for the party in a Wall Street Journal op-ed.
Then came the counter-strike. A coalition of liberal groups, united under the progressive banner, struck back with a political assault on members of Congress who support Third Way.
Make no mistake: This is bigger than a dispute over entitlement programs. This is a battle between the heart and brain of the Democratic Party. The "heart" are the progressives, the left-leaning populists who feel the country ought to strengthen its shabby safety net, rein in corporate America and raise taxes on the wealthy to promote a fairer society.
The "brain" are the moderate Democrats who believe that sharing the pie requires growing it first; that wealth creation in America is an answer for poverty, not the cause of it; and that the progressive agenda is a near perfect recipe for electing more Republicans.
The heart wants a much higher minimum wage, because people working 40 hours a week in a rich country should be able to live a dignified life on what they earn.
The brain says that America's low-skill workers are being replaced by automation and by cheap labor around the globe. If we force employers to pay $12 an hour for American workers whose skills command only $7 in the market, we will merely speed up the process by which the most vulnerable members of the labor force are displaced.
And so on. If you recall what Mitt Romney had to do and say to win the Republican primary in 2012, you can imagine the Democratic equivalent, with the progressive versions of Michele Bachmann and Rick Perry forcing more viable candidates to spout promises that are unpalatable to the general electorate. (More Social Security benefits for everyone!) Meanwhile, Warren may not be running for president, but she gives very good speeches from the sidelines.
This phenomenon — with Republicans pulled right by the tea party and Democrats pulled left by the progressives — could lead in two radically different directions.
The first is really bad. With each party beholden to its flanks, the possibilities for constructive compromise will shrink further. The pragmatists will be marginalized. The capacity of Congress to do anything meaningful will wither.
Here is the more heartening scenario (if less likely). The political tails could end up emboldening the center. Moderate Republicans may end up having more in common with moderate Democrats than they do with the tea party (and ditto for moderate Democrats and the progressives). A logical equilibrium would be three parties rather than two: one left, one center, one right.
Americans don't think this is crazy. In a Gallup Poll earlier this year, 60 percent of Americans agreed with the statement that "the Democratic and Republican parties do such a poor job of representing the American people that a third major party is needed."
If the extremists in both parties drive the rest of us into the middle, they could end up doing the country an inadvertent favor. Here's to hoping.