While your Insiders will follow the day-to-day combat of the 2012 race, every now and then it’s good to remember that all this is leading to the main event of Nov. 6.

As I often say, in American politics, what is supposed to happen tends to happen. Therefore, again, as I’ve said, you would have to bet on President Obama’s reelection if you had to bet today.

A professor at Yale has come up with a formula that calculates the probability of Obama’s reelection much more precisely than does my own simpleton analysis. There are various forms of these calculators and predicting models that come and go, but this one is as good as any I’ve seen. It largely relies on economic data, and Professor Ray Fair has reverse-engineered the formula to test its forecasting accuracy for every election since 1916.

It’s hard to argue with his approach. Professor Fair’s formula, factoring in modest GDP growth and inflation and no shift in party allegiance, gives President Obama a 54 percent probability of winning reelection. However, the model doesn’t account for the big problem that will never be reliably predicted by the analysts and pundits: the cancerous problem of low voter turnout for Obama and the entire Democrat ticket. The iceberg that could sink the president and the Democrats will not be seen until after Election Day.

The president won in 2008 in large part because he recruited many new first-time voters to the polls. Diminished enthusiasm will mean that many of those voters will not be second-time voters; some who do return to the polls regret their 2008 decision and will vote for President Obama’s opponent.

Also, the professor’s formula doesn’t account for what I fear could be the Republican’s iceberg: a third-party conservative or libertarian candidate who could sink our ship.

As the Republican contest clearly becomes meaner, it could produce more unhappy losers who may not go away quietly.