Rupert Cornwell: Events in Washington prove once again that after 10 years in power, your time is up

He or she may have won wars, transformed a party and brought unmatched prosperity to the people. But after a while the politicians abuse their power, the people become weary of them, or a combination of both. In a democracy, the cycle is unbending. Here in the US we are witnessing a perfect example of the process, with the criminal indictment for alleged campaign funding offences of Tom DeLay, the hitherto omnipotent leader of the Republican majority in the House of Representatives.

I make no bones about it. I cannot abide DeLay, his ruthless ways and narrow conservative views, all wrapped in the cloth of God. For me, he is emblem of much that is wrong with US politics. Arguably, though, he is the most powerful man in Washington apart from George Bush himself. A colleague once described DeLay as a cross between a concierge and a mafia don: "They can get you anything you want but it will cost you." How delicious it is that he seems to have received his comeuppance - those who live by the sword die by the sword, and all that.

But my personal views are beside the point. The point is that Mr DeLay is at the helm of a Republican party that has held power on Capitol Hill for more than a decade. And according to the 10-year rule, his (and its) time is up.

DeLay came in as part of the Newt Gingrich-led "Republican Revolution" at the 1994 mid-term elections. Gingrich won because the public felt that the Democrats had been in power too long and grown corrupt and lazy in the process. But in the 11 years since, the Republicans have trodden an identical path. Over that period, Tom DeLay, to friends and foes known as "The Hammer", has made the legislative part of the US constitution dance to his every wish.

Despite a venerated written constitution, and a vast legal system designed to protect that constitution, the fact is that the US system is more susceptible to manipulation and abuse than our own. DeLay would ignore congressional voting procedures to get contested bills through. Though the Republican majority was usually tiny, he largely shut the Democrats out of the legislative process. He let lobbyists help to write laws - so long as these latter poured money into the Republican campaign coffers.

The Democrats were furious but could do nothing. But in this arrogance, the assumption that power was inalienable and everlasting, lay the seeds of destruction. Even if Mr DeLay is exonerated, I would wager that this episode portends the defeat of the Republicans at the mid-term elections next year. Remember the 10-year-rule.

Naturally those who fall victim to this law don't see things that way. DeLay protests his innocence, convinced that once this little local difficulty is past, normal service will resume. Unlike American senators and congressmen, American presidents have no choice in the matter. Under the 22nd amendment they are limited to two four-year terms. But even they object.

I well remember Ronald Reagan, during his visit to Moscow in 1988, pleading to a group of Soviet students for a change in the constitution allowing him to run for a third term (which later that year he probably would have won, even though he had begun his descent into Alzheimer's). His audience, accustomed to the joys of a system where the same ruling elite perpetuated itself for all eternity, knew better.

Even Bill Clinton mused about a third term - or at least a change that would permit a two-term president to run again after a decent interval. But the 22nd amendment (passed after Franklin Roosevelt won a fourth term in 1944, only to die less than three months into it) gets it exactly right. As Thomas Jefferson, an early 19th-century two-termer, noted, "If some termination to the services of the chief Magistrate be not fixed by the Constitution, or supplied by practice, his office, nominally four years, will in fact become for life." Jefferson understood that power, if exercised too long, corrodes and corrupts. Politics at the highest level is not only an exhausting business.

It is apt to warp the mind and distort judgement - and nowhere more so than in the sealed-off world of the US presidency. But the 10-year-rule applies equally well in Europe. During the Cold War, the Italian communists were effectively barred from power for not 10, but 40 years. The price was a system where the same parties carved up the state for their own advantage, creating the most epically corrupt politics ever to masquerade as a Western democracy.

In Germany, when Helmut Kohl at last bowed out in 1998 after 16 years as Chancellor, he did so amid a scandal of kick-backs and influence peddling.

In our own dear land, Margaret Thatcher hit the brick wall when the appointed decade was up. As for her Conservative party, how much better would it have been to have lost the 1992 election after an already excessive 13 years, instead of staggering on for a disastrous five more?

In France, Jacques Chirac, elected president in 1995, has become a sorry living monument to the 10-year-rule. To his credit Tony Blair, feeling the grim shade tapping at his shoulder, acknowledges that his welcome is almost up. And so, more surprisingly (assuming we are to believe his promise he will not seek a third term), has Vladimir Putin in Russia.

And in the US? Tom DeLay and the congressional Republicans are already proving democracy's great law to be correct. So, too, in a fast-forward sense, is the man in the White House. Bush the son is surely the shallowest individual ever to hold his great office. Despite 9/11 and the invasion of Iraq, his has been an oddly content-less presidency. He has been in power for less than five years, but somehow it feels like double that.

Already, Bush seems a spent force, in Washington parlance a lame duck. The levels of cronyism, complacency and incompetence that normally take a government 10 years to achieve have been compressed into a far shorter period.

One reason he has got away with it thus far is that, to all intents and purposes, America is right now a one-party state, in which the Republicans have held both houses of congress as well as the White House, and the normal checks and balances of the constitution have not applied. But, I would wager, Tom DeLay's downfall - or more exactly the implacable 10-year-rule behind it - means that everything is about to change.