A Congress with no room for Olympia Snowe and other centrists?

Sniping and partisan acrimony inside Congress are evidently as bad as they seem from the outside, and Sen. Olympia Snowe would be first to second that.

Her decision not to seek a fourth term in the US Senate, announced Tuesday, has stunned lawmakers on both sides of the aisle. In a deeply divided Senate, Senator Snowe for years has been a key voice and a swing vote on issues ranging from tax cuts and economic stimulus plans to health-care reform.

But in the end, she cited partisanship, gridlock, and an inability to get things accomplished as not worth another six years of her career.

“An atmosphere of polarization and ‘my way or the highway’ ideologies has become pervasive in campaigns and in our governing institutions,” Snowe said in a statement on Tuesday. “It is time for change in the way we govern, and I believe there are unique opportunities to build support for that change from outside the United States Senate.”

Lawmakers willing to reach across the aisle are a vanishing species within the Republican Party – and are on the endangered list on the Democratic side of the aisle, as well. Nearly one-third of House Democratic centrists, or “blue dog” Democrats, aren’t running for reelection, including three top leaders. From 52 members in 2009, the blue dogs are down to 25 now – and their numbers are likely to sink lower after the November elections.

But the struggle is especially tough on the GOP side, where GOP moderates came to be viewed as less committed to conservative principles and were defeated in primary races by challengers to their right, or simply declined to run. When centrist Sen. Robert Bennett failed to make it into Utah’s GOP primary in 2010, moderate Republicans were stunned. This year, Sen. Richard Lugar of Indiana, a moderate with a celebrated record on arms control and foreign policy, is struggling to get past his 2012 primary race.

“Too many competent legislators have retired from Congress for the same reason as Senator Snowe. They’re sick and tired of being trapped in a rotten system,” said Mark McKinnon, a cofounder of No Labels, a public-interest group promoting bipartisan solutions, in a statement. “No Labels shares Senator Snowe’s frustration with the polarization and gridlock that is gripping Capitol Hill.”

In 2010 and 2011, Congress could find no political center – that is, not one Republican voted more liberally than any Democrat, and not one Democrat voted more conservatively than any Republican, according to a survey released this month by the National Journal, which has ranked voting records of Senate and House members for 30 years.

This year’s crop of Senate retirements, including lawmakers with a strong record of work across party lines, only deepens that rift. Those opting out include:

• Sen. Ben Nelson (D) of Nebraska, who helped pass the Bush tax cuts and was the last holdout on health-care reform on the Democratic side of the aisle, before agreeing to back the bill.

• Sen. Jeff Bingaman (D) of New Mexico, who as chairman of the Senate Energy and Natural Resources Committee helped develop bipartisan compromises on tough issues – compromises often viewed as too bipartisan by party leaders and blocked from the floor.

• Sen. Kent Conrad (D) of North Dakota, who led efforts in groups such as the Gang of Six to develop a bipartisan compromise over raising the national debt limit and cutting deficits.

• Sen. Joseph Lieberman (I) of Connecticut, whose outspoken support of President Bush’s policy in the Iraq War prompted a strong primary challenge in 2006 and his eventual party switch to run as an Independent. He also endorsed Sen. John McCain (R) in the 2008 presidential race.

Citing similar concerns about toxic partisanship in the Senate, Sen. Lamar Alexander (R) of Tennessee stepped down in January as Republican Conference chairman, the No. 3 ranking leader. “Stepping down from leadership will liberate me to spend more time working for results on the issues I care most about,” he said in a letter to colleagues last September. “I want to do more to make the Senate a more effective institution so that it can deal better with serious issues.”

Elected first to the House of Representatives in 1978, Snowe joined a Republican caucus that had not been in the majority since the 1950s and, urged on by fellow freshman Rep. Newt Gingrich of Georgia, was beginning to claw its way back.

At the same time, a culture of working across the aisle to get things done had a strong place in the Republican Party. Moderate caucuses such as the Tuesday Group or MainStreet Republicans gave centrists an identity apart from strict partisan lines and a base for proposing bipartisan solutions.

For a time, the closely divided Senate gave those remaining centrists an outsized role. But now, that prospect has faded. Snowe and Sens. Susan Collins (R) of Maine and Arlen Specter of Pennsylvania, then a Republican, were key brokers in President Obama’s 2009 stimulus bill. Their price: cutting $110 billion, reducing the final deal to $900 billion.

The outcome angered both Republicans, who opposed all stimulus spending, and Democrats, who feared that the cuts negotiated with GOP centrists made the final deal ineffectual. Mr. Obama has since backed off plans to negotiate with Republicans a “grand bargain” on debt- and deficit-reduction, opting instead to take disputed issues to the voters in November.

“The kind of elusive bipartisanship that President Obama wanted at the beginning of his term and that Senator Snowe thought was possible really isn’t,” says Julian Zelizer, a congressional historian at Princeton University. “You’re just not going to get very many bipartisan deals.

“Politicians aren’t in the business to lose. If they keep losing they step down,” he adds. “The partisans stay in there and win, and the centrists fade away. You will end up with a Senate after 2012 where partisanship will be that much stronger.”