The presidential campaign has been going on for what seems like six White House terms, but one of the key figures is just showing up now: the $100 barrel of oil.

It could be more significant than the $1,000-a-plate fundraising dinner.

Even if the comparison seems crude.

Relentlessly, oil prices are seeping toward triple digits, a milepost likely to rank with the 10,000 Dow and the $10 martini. This oil flow has already carried gasoline past $3, and the tide could run higher.

“It wouldn’t be out of the question to see $4 in some places,” AAA spokesman Geoff Sundstrom told Reuters recently, “if we stay at $95 to $100 per barrel of crude.”

Where it seems, for the moment at least, we’re parked.

Thursday, a barrel of West Texas Intermediate – the Champagne of unrefined petroleum – went to $97.49 on the New York Mercantile Exchange. In recent days, the barrel price has topped $98, and reaching a price beginning with “1” could happen well before Americans fill up to drive to Grandma’s house for Thanksgiving.

The price has been rising like a gusher. A year ago, a barrel was $58.93; in August, it was $72. Now, it’s heading past the normal human temperature of 98.6.

At about 105, of course, the brain starts to boil.

Not to mention the economy.

But even then might not be the ideal time to sell the barrel you’ve been keeping in your basement for investment purposes. Japanese expert Akio Shibata told the Japan Times this week, “It is highly possible that oil prices will test $120 to $130 a barrel.”

At that point, gas stations start to sell unleaded not by the gallon but by the cupful.

By now, everybody can recite the reasons the crude oil price list is beginning to resemble Bill Gates’ tax return. Demand from China and India is increasing sharply. The oil still out there costs more to recover.

And, of course, every time the vice president talks grimly about how the United States needs to take a firm line with Iran, the price shoots upward, since everybody knows what that means.

The foreign policy effect on the oil market hasn’t been exactly what it was supposed to be five years ago, when Rupert Murdoch, owner of Fox TV and much of the rest of the media world, explained that the meaning of toppling Saddam Hussein would be oil at $20 a barrel.

Another problem is the steady weakening of the U.S. dollar, making oil prices go up faster here than in Europe or Japan, and causing investors to get out of dollars and into euros – or oil.

“The big fear here,” Bart Melek, senior economist of BMO Capital Markets, told Market News International, “is that the dollar is going to hell.”

Put that in your gas tank and smoke it.

“In terms of the economy, we’re in uncharted territory,” David Sandalow, senior fellow of the Brookings Institution, said Thursday, just back in Washington from touring for his new book, “The End of Oil.”

But in terms of a nation realizing its situation and what it needs to do about it, he says, 100 could be a major landmark.

“It’s already happening, and I think $100 will spur it more,” says Sandalow. “Everywhere I go, there’s huge enthusiasm for this. Everybody on all sides is looking to get off oil.”

In 2010 or 2011, he says, General Motors will release the Chevy Volt, a car that can be plugged into the electric grid – which he calls a considerable change for the company that long ago stopped the electric car.

Sandalow sees the issue rising in next year’s politics, a position already staked out by New York Sen. Hillary Clinton’s support for plug-in hybrids in her energy policy.

“Iraq will be the biggest issue,” Sandalow concedes, “but the economy and energy will be the No. 2 issue.”

Sometime soon, the evidence will be inescapable that we need to make a sharp change of direction, and the oil market’s signal will be clear:

At $100, it will roll out the barrel.