In a print column yesterday, I suggested, in the spirit of contrarianism, that your typical U.S. president is a hostage of the economic cycle, rather than its master.

In this era of the imperial presidency, many Americans tend to assume, erroneously, that a chief executive blessed by boom times deserves most of the credit, and that if the economy is rotten, he deserves the brunt of the blame. But, as I sought to point out, reality is far more complicated, starting with the fact that presidents don't even have the clout to rein in the stubbornly independent Federal Reserve, which basically sets the nation's monetary policy.

That's as far as I took the theme in print, where space is finite. But here's an ancillary irony: Even though presidents truly lack the clout to change the domestic economy, the condition of the domestic economy is often a major factor in the selection of presidents. In good times, voters tend to reward the incumbent party; in bad times, voters tend to reward the out party.

If that's still true, one would assume that the prevailing winds of 2008 favor Barack Obama...unless he fails to heed the dangers that often stalk Democrats in the dog days of August.

One prominent political forecaster is economist Ray Fair of Yale. He argues that voter behavior is closely tied to the health of the economy (or lack thereof); by measuring various economic indicators - such as Gross Domestic Product, the economic growth rate in the first three quarters of an election year, and the rate of inflation - he claims to be able to roughly predict the popular vote of the two major party candidates. His record hasn't been perfect, but, on the average, he has come within 2.5 points of the winning candidate's popular vote share dating back to the 1916 election. (Some of his ruminations are here, for those of you who like this stuff.)

Naturally, Fair has a take on 2008. His current prediction is that, given the weak performance of the economy, as evidenced by the tepid GDP growth in the first two quarters of the year (0.9 percent and 1.9 percent), the election in November will be won by Obama. Fair sees a three-point Obama victory, 51.5 to 48.5 percent. (That would hardly be a landslide; on the other hand, the last time a Democrat managed to break 50 percent was 1976.)

The big question, however, is whether Americans in 2008 will vote their wallets and pocketbooks - assigning blame, as Fair sees it, to the incumbent party's nominee - or whether they will continue to confound conventional wisdom, as they have so often in this campaign season.

Indeed, one of the key reasons for McCain's recent barrage of attacks on Obama is his urgent need to change the traditional paradigm. His strategists are well aware that the sour economy hampers their prospects, especially since McCain is widely perceived in the polls as ideologically sympatico with the incumbent president of his own party; and since McCain himself has admitted that "the issue of economics is not something I have understood as well as I should."

Hence his need to make the voters focus on something besides economic anxiety. The obvious alternative - for a McCain attack team now dominated by Karl Rove alumni - is to shred the opponent's persona...and suggest, for example, that Obama is merely an uppity arrogant airhead celebrity who wants to lose a war.

And that's just for starters. It's August now, the traditional Democratic disaster month. Michael Dukakis was destroyed in August '88, when the GOP painted him as a water-polluting, insufficiently flag-waving, rapist-enabling wussy; his response at the time was zilch, because he refused to believe that voters would buy the caricatures. They did. And 16 years later, in August '04, John Kerry was transformed by the Swift Boaters from war hero to fraud; his response at the time was to embark on a wind-surfing vacation. His people said virtually nothing for several weeks, because they refused to believe that voters would buy the caricature. They did.

Obama now faces many potential dog day afternoons. His current line is that he is "disappointed" in McCain for launching such attacks, but I doubt that a mournful sigh is sufficient to stop further shelling from the McCain war room. Clearly he will need stronger weaponry if he wants to survive the ides of August. Contrary to what some of the economic forecasters believe, I find it hard to imagine, in this unconventional campaign season, that swing voters will tilt Democratic merely because of the sluggish quarterly growth rates in the GDP.