Editor's note: John Avlon is a CNN contributor and senior political columnist for Newsweek and The Daily Beast. He is co-editor of the new book "Deadline Artists: America's Greatest Newspaper Columns."
(CNN) -- The Vital Center is under siege on Capital Hill. "Congress is now more polarized than at any time since the late 19th century," attests the data-driven blog Vote View.
It has gotten so bad that Sen. Olympia Snowe is throwing in the towel on her three-term career in disgust: "I do find it frustrating," she said, "that an atmosphere of polarization and 'my way or the highway' ideologies has become pervasive in campaigns and in our governing institutions."
What's worse, she doesn't think it's going to get better any time soon: "I do not realistically expect the partisanship of recent years in the Senate to change over the short term."
It's just the latest confirmation of what you know in your gut: Our politics have become hijacked by hyper-partisans. Our divided Congress is dysfunctional. Our government is broken.
The Maine Republican's comments echoed Indiana Democrat Evan Bayh's statement when he announced he wouldn't seek re-election in 2010:
"For some time, I have had a growing conviction that Congress is not operating as it should," Bayh said. "There is much too much partisanship and not enough progress. Too much narrow ideology and not enough practical problem solving."
How many times will we need to hear the same refrain before we start taking these warnings seriously? Snowe's announcement follows Nebraska Sen. Ben Nelson's decision to not run for re-election after being attacked for compiling a record as the most conservative Democrat left in the Senate.
Independent Sen. Joe Lieberman, Al Gore's pick for vice president and John McCain's close ally, has also announced his retirement, for similar reasons. In 2006, Lieberman found himself under attack from the left for his post-9/11 support of the Bush War on Terror and won re-election as an independent after a lifetime as a centrist Democrat.
Conservatives have long gloried in the sport of RINO-hunting, trying to defeat what they call "Republicans In Name Only" in closed partisan primaries. Longtime centrist Republican Sen. Dick Lugar is the latest to be targeted in this cycle. Now liberal Democrats are trying to get into the game. These professional partisans believe the cure for what ails our political system is further polarization.
They are peddling a view of politics as an all or nothing ideological war, the strategy: mutually assured destruction.
Certainly, the ranks of centrist Republicans, operating in a grand tradition dating back to at least Theodore Roosevelt, have been diminished.
The number of northeast Republicans remaining in Congress can be counted on two hands.
Likewise, the ranks of Blue Dog Democrats -- resurgent during the New Democrat centrism of the Clinton years -- have been cut in half. North Carolina's Heath Shuler, who worked across the aisle most recently to try to achieve a grand bargain with a $4 trillion deficit reduction, won't run for re-election. Neither will Oklahoma's lone Democratic congressman, Rep. Dan Boren.
"It is not surprising to hear the news of Sen. Snowe's retirement," Boren e-mailed me. "She, like many of us in the center, have watched with dismay the further polarization of our politics. This is caused by an out of control campaign finance system which includes super PACs, the gerrymandering of congressional districts and a Congress that puts party above the national interest at almost every turn."
Republicans might soon learn to regret the departure of centrists like Olympia Snowe for purely practical reasons: Their attempts to take back control of the U.S. Senate in the 2012 election just got a lot tougher. Snowe was hugely popular in her home state despite some tea party grousing. It is, after all, one of the states where registered independents outnumber Democrats or Republicans. But now her seat is likely to be won by a Democrat, leaving Republicans fighting to pick up another.
A half century ago, congressional voting patterns resembled a bell curve -- with some congress members voting on the far left and far right, but most clustered in the center. Not coincidentally, this also reflected the spread of political opinions held by most Americans.
There were liberal Republicans and conservative Democrats. The result was that creative cross-aisle coalitions could be formed to pass major legislation. During divided government in the past, we passed the Marshall Plan and the Interstate Highway System. All the Reagan administration legislative accomplishments were passed with divided government -- the same was true of welfare reform and the balanced budgets of the Clinton years.
But now divided government means dysfunctional government. There is no trust and little cooperation. As a result, Congress has the lowest approval ratings on record. They cannot reason together and solve problems.
The departure of centrists like Snowe will make that job much harder in the foreseeable future. Their frustration with the status quo should be a huge wake-up call to the moderate majority of Americans.
The two parties may be polarized, but the American people are not. We need to send that message loud and clear to the professional partisans who are invested in polarization.
Make no mistake, the dysfunction will not get better until we change this corrosive culture of conformity in our politics.
"I see a vital need for the political center in order for our democracy to flourish and to find solutions that unite rather than divide us. It is time for change in the way we govern," said Snowe in her statement. "We must return to an era of civility in government driven by a common purpose to fulfill the promise that is unique to America."
I'll devote my next column to some ways we can start to push back on the dysfunctional congressional culture the hyper-partisans have created.
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The opinions expressed in this commentary are solely those of John Avlon.