“We have been studying Washington politics and Congress for more than 40 years, and never have we seen them this dysfunctional,” wrote Thomas Mann and Norman Ornstein in the Washington Post. “In our past writings, we have criticized both parties when we believed it was warranted. Today, however, we have no choice but to acknowledge that the core of the problem lies with the Republican Party.”

In Washington, “Mann and Ornstein” are a brand. Mann works at the centrist Brookings Institution; Ornstein at the conservative American Enterprise Institute. Over their four- decade partnership, they have established themselves as the two most respected, committed scholars — and defenders — of the U.S. Congress. They never tire of pointing out that the way the Founders designed the federal government, Congress came first, and it was intended to have an “institutional identity,” not a partisan identity. It’s that institutional identity, they now say, that is under threat, and more from one party then the other.

Their cri de coeur hit a nerve. The column, published two weeks ago, was recommended more than 241,000 times on Facebook. It generated more than 5,000 comments. It was tweeted more than 3,000 times. It made many Republicans very, very angry. But if you want to see why Mann and Ornstein wrote it, look no further than Senator Richard Lugar’s concession statement Tuesday night, which showed, in its wan effort to make the two parties sound equivalently extreme, just how much further the Republican Party has gone, and how right Mann and Ornstein were.

Here’s Lugar, after losing to Indiana Treasurer Richard Mourdock in the Republican primary:

“I don’t remember a time when so many topics have become politically unmentionable in one party or the other. Republicans cannot admit to any nuance in policy on climate change. Republican members are now expected to take pledges against any tax increases. For two consecutive presidential nomination cycles, GOP candidates competed with one another to express the most strident anti-immigration view, even at the risk of alienating a huge voting bloc. Similarly, most Democrats are constrained when talking about such issues as entitlement cuts, tort reform and trade agreements.”

First, note the policies he highlighted on both sides: Republicans have radicalized on climate, tax and immigration — by any measure, three of the most significant policy problems the country faces. Meanwhile, “most” Democrats are constrained when talking about entitlement programs, tort reform and trade agreements.

Wrong Animal

“Entitlement programs” — fine, that’s a big one. But tort reform and trade agreements? It’s like saying Republicans ignore the elephant in the room while Democrats have trouble talking about the guinea pig.

It’s not even true. You’ll notice that Lugar was careful in his phrasing. Republicans “cannot admit to any nuance” on climate change, they are “expected to take pledges” forswearing any tax increases, and they “competed with one another to express the most strident anti-immigration view.” Meanwhile, “most Democrats are constrained when talking about such issues as entitlement cuts, tort reform and trade agreements.”

“Cannot admit” is not the same as “constrained from talking.” It’s not even close, actually. Lugar, a senator known for his deliberate demeanor, clearly chose his words with care. Democrats might be “constrained” when talking about these issues, but they do it. Obama, for instance, has signed free- trade agreements with Colombia, Panama and South Korea. He told CBS’s “60 Minutes,” “I don’t believe malpractice reform is a silver bullet, but I’ve talked to enough doctors to know that defensive medicine may be contributing to unnecessary costs,” and he said in his 2011 State of the Union address that he’d be open to “medical malpractice reform to rein in frivolous lawsuits.”

As for entitlements, Democrats cut $500 billion from Medicare in the Affordable Care Act and created an appointed board designed to make far-reaching, cost-saving reforms to Medicare on an accelerated schedule. You may or may not like those changes, but they’re definitely “entitlement cuts” to Medicare, as Republicans, who successfully campaigned against them in 2010, know full well.

In his August 2011 negotiations with Speaker John Boehner, Obama broached raising the eligibility age for Medicare and slowing the growth in Social Security benefits by “chaining” the program to the consumer price index. At the end, those negotiations fell apart not because Obama couldn’t persuade Democrats to sign onto entitlement changes, but because Boehner couldn’t persuade Republicans to sign onto tax increases. More recently, Senator Kent Conrad, who is chairman of the Senate Budget Committee, proposed the Simpson-Bowles deficit-reduction plan as the Democrats’ long-term budget proposal, with the support of his party’s Senate leadership.

Systemic Effort

Then, of course, there’s the simple fact that Lugar was in a position even to write this concession speech. Over the past three years, there’s been a systematic effort uniting crucial parts of the conservative infrastructure to cull the Republican Party of legislators who are willing to compromise with Democrats.

Groups such as Americans for Prosperity and the Club for Growth. They targeted Mike Castle in Delaware, Bob Bennett in Utah, Arlen Specter in Pennsylvania, Lisa Murkowskiin Alaska, Olympia Snowe in Maine, Orrin Hatch in Utah and, of course, Lugar.

This has exerted a polarizing force on the Republican Party that simply doesn’t exist in today’s Democratic Party. Indeed, Senate Democrats chose to permit Joe Lieberman, who went much further than any of these Republicans in undercutting his party — even endorsing the Republican presidential nominee, John McCain, in 2008 — to keep all of his committee assignments. The move angered liberal activists who had organized a primary challenge to Lieberman in 2006. But just as primary campaigns from the right have shown Republican moderates that they must hew closer to the party line, the Democratic leadership’s embrace of Lieberman proved to Democratic moderates that the party would permit dissension.

The political scientists Keith Poole and Howard Rosenthal provide some independent empirical confirmation of the two parties’ “asymmetric polarization.” They’ve developed a system for tracking congressional polarization all the way back to the first congresses. Their research shows that the “median Republican and Democrat has moved toward their respective ideological poles in the contemporary period, but this effect is considerably larger in the House than the Senate and for Republicans more than Democrats.”

They’ve also found that since 2006, Democratic primaries where the incumbent lost and the challenger took office were as likely to end with a more moderate legislator holding the seat as with a more liberal one. In Republican primaries, 75 percent of the successful challengers were more conservative — and that’s without considering instances, such as Specter’s campaign in Pennsylvania, where a more conservative challenger drove an incumbent out of the race or into the other party.

Whether the Republican Party is “the problem” is a subjective judgment. Perhaps you loathe taxes and, in the face of all available evidence, consider global warming a hoax. In that case, the Republican Party is doing exactly what it should be doing. But there is simply no denying that the Republican Party has gone much further right than the Democratic Party has gone left, and that, from policy pledges to primary challenges, it has done much more to discourage its members from compromising than the Democratic Party has. So if you think polarization is the main problem in Washington today, then Mann and Ornstein are right: Your beef is largely with the Republicans.

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Follow Ezra on Twitter @ezraklein. Ezra Klein is the founder and editor-in-chief of Vox.com.