Finally, finally, finally. A few years back, your correspondent noticed something a little odd about George W Bush’s conservatism. If you take Margaret Thatcher’s dictum that a socialist is someone who is very good at spending other people’s money, then President Bush is, er, a socialist.

Sure, he has cut taxes, a not-too-difficult feat when your own party controls both houses of Congress. But spending? You really have to rub your eyes, smack yourself on the forehead and pour yourself a large gin and tonic. The man can’t help himself.

The first excuse was the war. After 9/11 and a wobbly world economy, that was a decent excuse. Nobody doubted that the United States needed to spend money to beef up homeland security, avert deflation, overhaul national preparedness for a disaster, and fight a war on terror. But when Katrina revealed that, after pouring money into both homeland security and Louisiana’s infrastructure, there was still no co-ordinated plan to deal with catastrophe, a few foreheads furrowed.

Then there was the big increase in agricultural subsidies. Then the explosion in pork barrel spending. Then the biggest new entitlement since Lyndon Johnson, the Medicare drug benefit. Then a trip to Mars. When you add it all up, you get the simple, devastating fact that Bush, in a mere five years, has added $1.5 trillion to the national debt. The interest on that debt will soon add up to the cost of two Katrinas a year.

Remember when conservatism meant fiscal responsibility? In a few years, few people will be able to. I used to write sentences that began with the phrase: “Not since Lyndon Johnson’s Great Society spending binge. . .” I can’t write that any more. Johnson — the guns and butter president of liberalism’s high-water mark — was actually more fiscally conservative than the current inhabitant of the White House. LBJ boosted domestic discretionary spending in inflationadjusted dollars by a mere 33.4%.

In five years, Bush has increased it 35.1%. And that’s before the costs for Katrina and Rita and the Medicare benefit kick in. Worse, this comes at a time when everyone concedes that we were facing a fiscal crunch before Bush started handing out dollar bills like a drunk at a strip club. With the looming retirement of America’s baby-boomers, the US needed to start saving, not spending; cutting, not expanding its spending habits.

This was one reason I found myself forced to endorse John Kerry last November. He was easily the more fiscally conservative candidate. Under Clinton, the US actually ran a surplus for a while (thanks, in part, to the Gingrich-run Congress). But most conservatives bit their tongues. Bush promised fiscal tightening in his second term and some actually believed him.

They shouldn’t have. When Bush casually dismissed questions about funding the $200 billion Katrina reconstruction with a glib “It’s going to cost what it costs”, steam finally blew out of some loyal Republican ears. When the house majority leader Tom DeLay told the conservative Washington Times that there was no fat left to cut in the budget and that “after 11 years of Republican majority we’ve pared it down pretty good”, a few conservatives lost it.

Here’s the chairman of the American Conservative Union: “Excluding military and homeland security, American taxpayers have witnessed the largest spending increase under any preceding president and Congress since the Great Depression.” That would be correct. When you have doubled spending on education in four years, launched two wars and a new mega-entitlement, that tends to happen.

Here’s Peggy Noonan, about as loyal a Republican as you’ll find, in a Wall Street Journal column last week: “George W Bush is a big spender. He has never vetoed a spending bill. When Congress serves up a big slab of fat, crackling pork, Mr Bush responds with one big question: Got any barbecue sauce?”

Here’s Ann Coulter, the Michael Moore of the far right, a pundit whose book on liberalism was titled Treason: “Bush has already fulfilled all his campaign promises to liberals and then some! He said he’d be a ‘compassionate conservative’, which liberals interpreted to mean that he would bend to their will, enact massive spending programmes, and be nice to liberals. When Bush won the election, that sealed the deal. It meant the Democrats won.

“Consequently, Bush has enacted massive new spending programmes, obstinately refused to deal with illegal immigration, opposed all conservative Republicans in their primary races, and invited Teddy Kennedy over for movie night. He’s even sent his own father to socialise with ageing porn star Bill Clinton.” Ouch.

Conservatives have been quietly frustrated with Bush for a long time now. Honest neoconservatives have long privately conceded that the war in Iraq has been grotesquely mishandled. But in deference to their own party, they spent last year arguing that John Kerry didn’t deserve his Vietnam war medals. Social conservatives have just watched as the president’s nominee for chief justice of the Supreme Court pronounced that the constitutional right to abortion on demand merited respect as a legal precedent. This hasn’t cheered them up. The nativist right, long enraged by illegal immigration, has been spluttering about foreigners for a while now. But since few want to question the war publicly, oppose the president’s nominees to the court, or lose the Latino vote, the spending issue has become the focus of everyone’s discontent.

All I can say is: about time. I believe in lower taxes. But I also believe in basic fiscal responsibility. If you do not cut spending to align with lower taxes, you are merely borrowing from the next generation. And if a Republican president has legitimised irresponsible spending, what chance is there that a Democrat will get tough?

This may, in fact, be Bush’s real domestic legacy. All a Democratic successor has to do is raise taxes to pay for his splurge, and we will have had the biggest expansion of government power, size and responsibility since the 1930s. What would Reagan say? What would Thatcher? But those glory days are long gone now — and it was a Republican president and Congress that finally buried them.