"There is a tide in the affairs of men / Which, taken at the flood, leads on to fortune." But tides also recede. The big question for observers early in this election year is: Has the tide finally turned?

Still running John Howard's way are the economy and the resources boom, as well as the momentum of incumbency. But there are also powerful currents pulling the other way, deeper than the surface froth of political debate and the play of issues. There are three turning points with the potential to shift the basis on which Howard has built his political success: from age to youth; from fear to hope; from private to public.

From age to youth. This is the most obvious. When he turned 65, Howard promised to stay in the job for as long as the Liberal Party and the voters wanted him. And he reiterated the promise when Costello challenged last year. There is a deep disingenuousness in this promise. Taken at face value - and this is how Howard wants it taken - it disavows personal ambition and puts him at the service of the party and the nation. But it also says, If you want me to leave, you will have to throw me out. Hence Keating's rather improbable image of Howard as a coconut glued to his chair, and his reminder of the brutality of his own disposal of Hawke. "You know, prime ministers have got Araldite on their pants, most of them. They want to stick to their seat. And you either put the sword through them or let the people do it."

Howard, of course, will argue for the benefits of experience and a wise head. But whatever he says or promises, he cannot escape the fact that he is getting old. And all of a sudden, with Rudd rather than Beazley as his opposite number, he looks it. Howard turns 68 in July this year. When the next election comes round, in 2010, he will be 71. What is he to say to the electorate about his intentions? Elect me and I promise to say on till I'm 71, and then I may even run again, like my hero Robert Menzies, who stayed on till he was 72! Or: Elect me, and at some unspecified date before the next election, I will retire and pass the leadership on to my loyal and patient deputy, he of the down-turned mouth, who lacks the common touch and already looks worn out from all those hard years in Treasury.

Old leaders often believe that after them, the deluge: it seems to be a hazard of the psychology of ageing. So, on the whole, they stay on too long. It would have been much better for Menzies' subsequent reputation had he lost the credit squeeze election in 1961 (which he won on Communist preferences); for Margaret Thatcher not to have waited till she was pushed; for Mao Zedong not to have launched the Cultural Revolution. At stake here is not just the age of leaders and their waning physical and intellectual energy, but their inevitable disconnection from the social and cultural worlds of people born 20, 30, 40 and even 50 years after them - and from their futures. Sometimes, ageing leaders are reckless with their country's future because they won't be around to bear the consequences. So Howard seems remarkably unworried about the consequences of global warming, responding to it more as a political challenge to be managed than a real-world danger.

From Fear to Hope. Critics of Howard argue that much of his political success is due to the way he has used fear: fear of asylum seekers, terrorists, rising interest rates, loss of jobs and so on. The most sustained argument for this is found in Carmen Lawrence's book Fear and Politics, and it is a standby of the so-called Howard-haters. I don't completely agree with this position: it is overblown, and relies on a sloppy conflation of Howard's characteristics with those of the Australian people. Because it interprets Howard's political success in essentially negative terms, it fails to engage with the full range of reasons why voters have supported the Coalition. The Coalition has always been the preferred party of the cautious, and caution is not the same as fear. However, I think a slightly different and more complex claim takes us to the heart of Howard's prime ministership.