Forbes columnist Peter Cohan says he was paying $4.50 a gallon for gasoline last spring but that now the price has dropped to $3.49 a gallon. That cost difference would save him $582 a year, says Cohan, and when you aggregate those savings across the U.S. economy, they add $78.4 billion to GDP.

It seems a bit unusual for a journalist from the corporate press, but Cohan is more than willing to give credit where credit is due — he says the reduction in the cost of gas is a result of actions taken by Pres. Obama earlier this year:

In April, I predicted that Pres. Obama’s $52 million plan to increase the margin requirements and otherwise tighten the screws on oil speculators — who borrow huge sums to bet on the direction of oil without taking delivery — would cut oil prices by 10%. He’s beaten that prediction and the lowered price of gasoline has added $78.4 billion to its consumers’ spending power.

In case you never heard about it, in April the Obama administration asked Congress to spend $52 million to regulate this speculation …

So what’s happened since April? Oil ended the month at $106 and as of June 22, it had lost 21 percent of its value — sitting at $84. I guess I under-estimated the impact of the CME’s boost in margin requirements for oil speculators.

Cohan lists other possible contributing factors including the strengthening of the dollar against the Euro and an expected surge of supply in oil markets.

When the prices were high back in the spring, in GOP debates, at tea party klatsches and on Fox, Republicans excoriated Pres. Obama, blaming his socialist, anti-Big Oil energy policies for the high price of gas:

[On Fox, Mitt Romney] said he “absolutely” believes Mr. Obama is responsible for high gas prices, contending that “he has not pursued policies that convince the world that America is going to become energy secure, energy independent.”

Senate Minority Leader Mitch McConnell (R-Ky.) lays the blame for rising gas prices on President Barack Obama, saying “he certainly has participated … This administration has been shutting down wells,” McConnell said on “Fox News Sunday.”

House Speaker John Boehner (R-Ohio) blamed President Obama and “radical environmental groups” for high gas prices on Tuesday and said it was “about damn time” the United States had a national energy policy.

Newt Gingrich made the high gas prices a major issue in his campaign:

“If you want $10-a-gallon gasoline, an anti-energy secretary and weakness requiring us to depend on foreigners for our energy, Barack Obama should be your candidate,” the former House Speaker told a crowd during a luncheon at the California Republican Party’s bi-annual convention.

Gingrich even promised to lower the cost to $2.50 a gallon when elected. No one expected him to explain how he would execute such a miracle because a) everyone knew there was no chance Gingrich would be elected and b) everyone know Newt is always, always wrong.