KEY POINTS:
UNITED STATES - There are cycles in American political life, argued historian Arthur Schlesinger. Spells of conservativism and private purpose alternate with periods of liberalism and public-spiritedness - with turbulent years of transition in between.
If the Schlesinger thesis has any validity, the US looks as if another such a transition is just beginning.
One signal of change is that the opinion-poll leader for the Republican party nomination, Rudy Giuliani, is a three-times married man who has marched in New York gay rights parades. Yet another is that the Democrat front runner is Hillary Clinton.
Behind these changes, as so many times in the past, is a swing in the cultural pendulum. The key indicator is religion, always important in the US.
For the past 25 years, an evangelical, militant, right-wing Christianity has been making the political and cultural weather. The high-water mark was November 2004 when nearly half the Senate and two-fifths of the House of Representatives could be claimed by the fundamentalists as fully bought in to their agenda - from anti-abortion to anti-stem cell research.
But since then the Christian right has found progress tougher, in part because of an embarrassing string of scandals, in part because secular America has begun to reassert itself, and in part because a growing number of American Christians are uneasy about allowing religion to become so politicised and so closely associated with one party.
Fundamentalist Islam has also made a difference, reminding the bulk of Americans of the wisdom of the American constitution - keeping religion and state firmly apart.
For two faiths coexist in the United States: one is devotion to God and the other to the Constitution. The genius of the founding fathers was to make sure that the two did and do not mix.
Religion is a private matter, with which the state is barred from interfering - and which is barred from interfering with the state.
Fundamentalist Christians have had ambitions to overturn that long-standing convention. This was the overt aim, for example, of the influential Rousas Rushdoony, founder of the home-school movement and author of The Institutes of Biblical Law, which argued that the US should be governed according to the 10 Commandments.
For years, Democrats have unsuccessfully attempted to demonstrate that personal faith does not need to include the urge to evangelise the whole country, and now the wider mood has changed in their favour. The Pew Research Centre reported last July that 49 per cent of respondents thought conservative Christians were going too far in imposing their religious values on the country.
While that doesn't sound terribly impressive, it is up from 45 per cent in 2005. And there are big majorities in favour of science and doubting that the Bible is the literal word of God.
The mood has been reflected by an extraordinary little book, Letter to a Christian Nation, by Sam Harris. It has become a bestseller.
Harris quotes passages from the Bible that I did not know existed, such as one in Exodus discussing the demands you should make when selling your daughter into slavery. One passage from Deuteronomy encourages Christians to stone to death anybody who tries to draw them away from their God.
As for governing America according to the 10 Commandments, Harris is withering; four do no more than outlaw other religions and the rest are a routine expression of core moral precepts. For a book which ridicules religion and ruthlessly exposes the inadequacies of the Bible to become a bestseller is a classic Schlesinger-style signal that times are changing.
And politicians are feeling the mood swing. Mormon Republican Mitt Romney's bid for the Republican presidential nomination is floundering despite his otherwise impressive credentials.
One of the key speeches Barack Obama made last year before announcing he was running for the Democrat nomination was at the Call to Renewal convention, a Christian group which declares independence from radical conservatism and focuses on the alleviation of poverty.
The best American leaders of the past had faith, Obama argued, but they had not tried to evangelise the nation, recognising that a plural society had to be based on mutual tolerance and universally applicable laws that cannot be theocratic. His standing soared.
Religion is not the only indicator. Other tipping points have been exceeded, for example the consensus that the US needs to act to limit the emissions of greenhouse gases.
It seems, with a little under two years to go, that the Democrats have the presidency for the taking - just so long as they make no disastrous gaffes and read the cultural runes properly.
- OBSERVER
