In war, luck is a definable quantity. Some generals — the type Napoleon famously preferred — are lucky. U.S. Grant referred constantly to his own luck as a military leader. Patton strongly believed in luck. Oddly enough, military luck seems to favour risk-takers and innovators.

But wars end, and few are the successful generals who get to fight the next war. In politics, if you stay in the game, eventually your luck turns bad.

John Howard, for example, was lucky for much of his term as Prime Minister. He’d been utterly unlucky during his first stint as Opposition Leader in the 1980s, but for his first three terms he was favoured by fortune — sneaking home in 1998 despite obtaining less votes than Labor; being handed the Tampa and September 11 for the 2001 election, having Meg Lees ready to sacrifice her party to get the GST through, having a prize galoot in Mark Latham for an Opposition Leader, and having a deputy too gutless to ever challenge him.

For a while, in the aftermath of the 2004 election and winning control of the Senate, Howard seemed destined for a permanent golden run. But in retrospect that was the exact moment his luck not merely ran out, but turned against him. Thereafter, he couldn’t take a trick. Indeed, just about every single piece of good fortune he’d ever had seemed to come back and bite him. National security scares turned into bungles. Interest rates went up. Howard was forced to give a leadership transition timetable. Liberals in Lindsay decided to have their own version of the Ralph Willis letter.

When Howard’s luck turned, it turned with a vengeance.

George W. Bush’s career tells the same story. Bush for a long time seemed eerily fortunate. He escaped any serious scrutiny of his draft-dodging during Vietnam, or of his terrible business record. And remember he stole the 2000 election not once but twice, launching one of the most appalling smear campaigns in presidential history against John McCain after McCain thumped him in New Hampshire. The election of McCain, a superior candidate at that point to both Al Gore and Bush, would at least have spared us the regency of Dick Cheney, who has inflicted profound damage on the world in the last eight years.

Bush even had the chance to start over after September 11, such was the outpouring of sympathy and fellow-feeling in the aftermath of the attacks. Remember Le Monde’s “Nous sommes tous les Americains”? But that spirit of goodwill and support was instead used to embark on a strategically — not to mention morally — disastrous war so unutterably stupid as to support the contention of a British diplomat that Bush was the best recruiting officer Al-qaeda could have.

Bush even got lucky in 2004, up against the unconvincing John Kerry, although he had to resort to another smear campaign to hold onto the presidency.

As with Howard though, that marked the end of his good luck, as if he had borrowed a whole lot of the stuff and now faced a margin call on his political fortune. And as with Howard, traits that once were strengths became fatal flaws. First his plans to partially privatise social security ran into the ground. The disaster of Hurricane Katrina showed up his administration’s cronyism and incompetence. And all the time, with a steady drip of body bags and uncounted civilian deaths, it was becoming clear how badly the occupation and reconstruction of Iraq was being handled. Bush’s leaking authority was undermined further in the controversy over Dubai Ports World and, after disastrous mid-term elections in 2006, on immigration reform.

Given all that, the meltdown of the US financial sector and a plunge into recession in the last days of Bush’s term look almost inevitable.

His turn in fortunes has spread out from the White House and into his own party. For a long while, John McCain — no longer the lunatic brainwashed in a Hanoi cell who had fathered a black child, but the party’s standard-bearer — managed to keep a distance from the profound damage inflicted by Bush on the Republican brand. But there was no escaping the stench of the financial meltdown, even if McCain had not mishandled his own response. What was a fighting chance around the time of the conventions has become a lay-down misere for Obama. And the damage has gone further, threatening a Senate and House electoral slaughter sufficient to hand full legislative control to the Democrats.

Political luck eventually turns if you stay in the game long enough.

Which Barack Obama should bear in mind. He is a lucky man. Not merely to find himself up against a crippled, indeed feeble, Republican party, but to be on the ticket at all. It is only because John Edwards kept his infidelity secret for as long as he did that Obama is there. But for Edwards’s lying, we would now be on the eve of the election of the first female president, Hillary Clinton, a candidate superior in every way to the man about to enter the White House.

Obama’s biggest piece of fortune, however, might be one he shares with Kevin Rudd. He’s got an economic disaster at the start of his time in office, and there’s no better way to instantly look like you’ve got the right stuff.