By E.J. Dionne Jr – The Washington Post.

The deficit that should most worry us is a deficit of reasonableness. The problems the United States confronts are large but not insoluble. Yet sensible solutions that are broadly popular can’t be enacted.

Why? Because an ideological bloc that sees every crisis as an opportunity to reduce the size of government holds enough power in Congress to stop us from doing what needs to be done.

Some of my middle-of-the-road columnist friends keep ascribing our difficulties to structural problems in our politics. A few call for a centrist third party. But the problem we face isn’t about structures or the party system. It’s about ideology — specifically a right-wing ideology that has temporarily taken over the Republican Party and needs to be defeated before we can have a reasonable debate between moderate conservatives and moderate progressives about our country’s future.

A centrist third party would divide the opposition to the right wing and ease its triumph. That’s the last thing authentic moderates should want.

Let’s look at the record, starting with the congressional supercommittee’s failure to reach agreement on a plan to reduce the fiscal deficit. It’s absurd to pretend that we can shrink the deficit over the long term without substantial tax increases.

No matter how hard policymakers try to trim spending on Medicare, its costs will go up for many years simply because so many baby boomers will be retiring between now and 2029. Moreover, employers will keep cutting back on coverage for their workers as long as the price of insurance continues to go up.

However we manage it, in other words, government will be required to pay an ever larger share of our nation’s health-care bills. That means the government’s share of the economy is destined to rise — unless we decide to leave a large part of our population with little or no protection against illness.

The least we can do under those circumstances is to repeal the tax cuts for the wealthy enacted under President George W. Bush. Yet the only revenue conservatives on the supercommittee put on the table involved $300 billion, most of it from ill-defined tax reforms, in exchange for lower tax rates on the rich and making something like $3.7 trillion worth of tax cuts permanent.

Progressives have already made clear that they are willing not only to increase revenue but also to cut Medicare costs. The Obama health-care law did both, and it was attacked by Republicans for doing so. Democrats on the supercommittee offered substantial entitlement cuts. But they rightly refused a deal that would squander years of future revenue in the name of keeping taxes low on the wealthiest Americans.

What might a reasonable budget argument look like? Progressives would propose fewer spending cuts in exchange for tax increases that would fall mainly on the wealthy: higher rates on top incomes, capital gains and estates, along with a financial transactions tax. Conservatives would counter with larger spending cuts coupled with taxes on consumption rather than on investment. Out of such a debate might come a sensible deal, based on a shared acknowledgment that long-term balance requires both thrift and new revenue.

In the meantime, a broad range of economists agree that America’s sputtering jobs machine needs a sharp and quick jolt. It is unconscionable that in the face of mass unemployment, Republicans continue to foil measures to spur employment, including an extension of the payroll tax holiday. How can conservatives declare simultaneously that (1) it would be a terrible crime to raise taxes on the rich in the long term, and (2) it is an act of virtue to raise taxes on the middle class immediately? Has class warfare ever been so naked?

Then there is immigration. Common sense says there is no way the United States can or should deport some 11 million illegal immigrants. But when Newt Gingrich spoke of this reality — and suggested that conservatives ought to worry about how deportations would break up families — he was said to have committed a gaffe that will end his ride as the Republican front-runner. In today’s GOP, it’s becoming dangerous to be sensible.

We need moderation all right, but a moderate third party is the one way to guarantee we won’t get it. If moderates really want to move the conversation to the center, they should devote their energies to confronting those who are blocking the way. And at this moment, the obstruction is coming from a radicalized right.