At the G8 in Germany this week President Bush played to perfection his assigned role of chief war criminal and global environment-despoiler, with an interesting new sideline as nasty bully of those nice, peaceable Russians.

With the President getting an earful abroad, back here in Washington, all eyes were on domestic politics. The big story of the week was the sentencing of “Scooter” Libby, Vice-President Dick Cheney’s former chief of staff, to an unusually harsh prison term for his role in a classic Washington scandal. Just as war is a continuation of diplomacy by other means, so in Washington the criminal law has become simply a rougher form of politics. In a litigious society, what you can’t achieve in elections, you can usually get from a friendly jury.

The case against Mr Libby was always murky. In true Washington style it was less of a whodunnit than a whodidn’tdoitbuttriedtocoveritup. He was charged and convicted with lying to a jury about a leak of information he may or may not have committed that wasn’t illegal in any case. Now Mr Bush will have to decide whether to extend the politicisation of the legal process by pardoning him.

But the most memorable aspect of Mr Libby’s sentencing was not the judge’s draconian view of it all, but the character witnesses Mr Libby called on in his plea for leniency. For reasons known only to himself, these included Donald Rumsfeld and Paul Wolfowitz, who wrote letters to say that Mr Libby was a man who enjoyed their highest esteem.

Given the standing of these men at this moment, it was a little like watching Lord Voldemort trying to defend himself with character testimonies from Sauron of Mordor and the White Witch from Narnia.

It was a depressingly revealing moment. This grisly litany of the unsaintly was an unfortunate reminder of just how low the Republicans have sunk these days. By the time President Bush leaves office, anyone who has not been disgraced or convicted will surely be eligible for some sort of medal.

So sorry is the Republican condition that there’s little doubt now, even 18 months out, that the 2008 presidential election is for the Democrats to lose. The only reason politics remains interesting is that in the past the Democrats have demonstrated an impressive capacity to stoop to the challenge – and somehow contrive to lose it. Can they possibly do so again?

The political conditions are uniquely favourable to them. In any ordinary circumstances, for a party to win a third straight presidential term in office, as the Republicans would have to do next year, is remarkably difficult.

In the past 50 years only George Bush Sr did it, after eight years of Ronald Reagan in 1988. Change for its own sake is not only the faddish prerogative of voters but democracy’s vital means of renewing itself. You don’t have to subscribe fully to Lord Acton’s dictum to believe that kicking the buggers out every few years is the best way to safeguard the constitution.

And that one example of a party winning three straight terms in 1988 came in exceptional circumstances. The country was at peace and remarkably content; Reagan, after a rocky patch, was beginning to be transfigured into the semi-mythological figure he would subsequently become.

This time around, the country is mired in war and deeply ill at ease with itself. Mr Bush is no Reagan. So for Democrats, these are abundant days. What could possibly prevent them from assuming their rightful inheritance next year?

There are, in fact, two small clouds, no bigger than a man – or perhaps a woman’s hand – on the horizon of this otherwise sunlit landscape for them.

The first is the candidate. If you ask voters the so-called “generic” question – do you want the Democrats or the Republicans to win the White House next year – the Democrats win by a mile. But if you put real names and faces on those generic party titles, something odd happens. The Republicans have the edge in most of the putative head-to-head matchups. Rudy Giuliani, John McCain, the suddenly fashionable actor-turned politician Fred Thompson, all win most of their putative contests against likely Democratic contenders. Why is this?

The main reason is that, for all the party’s large political advantages, the character of Democrat leaders still troubles many voters. Hillary Clinton has spent the past few months demonstrating why she has long been the party’s favourite for the nomination. She is experienced, knowledgeable, disciplined and self-assured. But she still makes the hairs on the backs of the necks of a surprisingly large number of Democrat-inclined voters stand on end. They just don’t like her, and don’t trust her chameleon-like political changes.

Barack Obama makes up for Ms Clinton’s weakness with voters by being almost inhumanly likeable, charming and excitingly new. But his lack of any real experience is a worry to voters who may not want to entrust their security to a man who just a few years ago was an ambitious local politician in Illinois. So, for the time being at least, many people say they’d prefer a Democrat – just not either of these.

The second obstacle for Democrats is Iraq. This seems counterintuitive, Surely, the war is primarily what is feeding the surge in support for the party? The problem is that the Democrats are dangerously close to the point at which they could be forced to switch from having power without responsibility for the war to having responsibility without power.

They’ve played a clever game so far of articulating opposition to the war without forcing Mr Bush to stop it. But it’s clear now that September will be the crunch time. Enough Republicans will be ready to ditch the war effort that the Democratic majority in congress will suddenly be free to do what it has threatened to do – cut off funding for the troops.

If the US begins a substantial drawdown of troops after that, and Iraq and the region descends into more chaos, the Democrats could easily find themselves suddenly to blame for a dwindling war effort and spiralling global insecurity over which they have no real control.

Certainly the Democrats are in the driving seat. But they’ve been there in the past and steered into a ditch. Surely they can’t mess it up again?

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