Blame not the heartless Republicans nor the spendthrift Democrats for the deficit. Blame instead the political class. Just when you thought there was no chance left and right could agree on anything, when you thought the primary colors red and blue could defy the natural world (where they meld quite nicely, which is why we have the splendid color purple) and clash in the political world (where the two colors repel each other), we have the biggest, the gaudiest, the most perfidious secret political agreement of our time.

Let’s face the truth: The Republicans and the Democrats are conspiring to create, to perpetuate and to luxuriate in the deficit. Theirs is a $427 billion achievement.

These distinguished solons of both sides haven’t actually gathered secretly in the Senate Caucus Room, nor sent secret plenipotentiaries to each side, nor even dispatched conciliatory cakes and Bibles to each other. They’re doing what comes naturally. Or what comes cynically. Same thing, now that you think about it.

A few days ago, the revered ancient mariner, Alan Greenspan, intoned the predictable diagnosis that the budget deficit was “unsustainable,” thereby ending yet another myth in the capital, the one that says that Washington listens to what the Federal Reserve chairman says. Not this time. Don’t expect either Republicans or Democrats to move a single billion off the deficit. They’ll spend a lot of time discussing whether trimming the deficit is in the national interest, but they know full well that sustaining the deficit is in their political interest. All of theirs.

It’s not my deficit

The Democrats aren’t disposed to ditch the deficit because they know it’s not their deficit. Just as the War of 1812 was Mr. Madison’s war, the deficit of 2005 is Mr. Bush’s deficit. Because it’s not their deficit, it’s not their problem. Indeed, it’s part of their solution. The bigger the deficit, the better their argument that the president is an irresponsible steward of the national economy, and (to borrow a phrase from the president’s father, no stranger to the dangers of the deficit straits), the beauty thing is that the midterm congressional elections aren’t that far away. This is the best issue since, well, Social Security.

But the Republicans, for all the peril the deficit poses for them, aren’t really against the deficit either. A federal budget deficit is a political tool. It’s a wedge and a bludgeon. For every new spending program the Democrats propose, there’s one handy answer: With a deficit this big, we can’t even begin to consider spending programs like this. Pretty good, no?

The bipartisan Concord Coalition believes that the deficit will only grow. The war on terrorism will add $418 billion in the next decade. (No one’s against that, and for good reason.) Extending the expiring tax cuts will account for $1.6 trillion growth in the deficit. (When exactly was the last time a tax cut was repealed?) Increased debt service will add $810 billion. (This is the most insidious and gratuitous form of governmental waste known to humankind.) The Concord Coalition’s analysis is that the deficit is likely to hover between $400 billion and $500 billion for the next five years.

Pretty soon we’ll be talking about real money.

This is something new under the sun. The last time the deficit was a big issue was in the Reagan-Bush years, when the Republicans held the White House and the Democrats still had some power on Capitol Hill. Now the Democrats are powerless (this phrase is not a metaphor), and the lack of shared responsibility leads to a lack of shared purpose.

One thing we know for sure: There won’t be a deficit summit this time like the one the first President Bush endorsed in 1990, the one that brought a tax increase and, it is easy to argue, the ascendancy of conservative insurgents and the end of the Bush presidency. The lessons from the last deficit aren’t pretty. Bush pushed for a budget deal and lost the 1992 election. Bill Clinton pushed through a deficit-reduction pact and lost control of the Congress. Two presidents make a bad precedent.

Some historical perspective

Now for a bit of sobriety. Things have been worse. The deficit as a percentage of gross domestic product was a lot higher in the Reagan years — 6 percent of GDP in 1983, as opposed to 3.6 percent last year. (It was 5.9 percent of GDP in the depression year of 1934 and 30 percent of GDP in the wartime year of 1943. Nobody compares those periods with ours.)

But as mild as our own deficit may seem, and as beguiling as the deficits-don’t-matter convictions may be, we have a substantial challenge in our own time.

The baby boomers are two decades closer to retirement now than they were in the Reagan-Bush years, and as a result the huge financial crisis that their retirement poses is that much closer. In the 1980s and 1990s this was a meteorite somewhere out there in the cosmos, maybe heading our way, maybe not. In the first decade of the 21st century, the meteor showers are visible to the human eye, and the only question is where the crater will be. Maybe in a home near yours.

The shrewdest political and economic thinker of the recent past didn’t stride through the pleasant groves of academe. He walked the marble halls of Congress. He was Russell Long, the Louisiana Democrat who for 16 years made the word “powerful” redundant with the phrase “chairman of the Senate Finance Committee.” He knew many things, but most of all he knew one thing, the way tax politics works: “Don’t tax you, don’t tax me. Tax that fellow behind the tree.”

The Long rule goes a long way toward explaining modern deficit politics, too: “Don’t blame you, don’t blame me. Blame that fellow behind the tree.” Right now everyone’s behind the tree.

— David Shribman is executive editor of the Pittsburgh Post-Gazette.