President Obama is taking on former Massachusetts governor Mitt Romney by name in a new campaign ad, the first time he has done so in the 2012 race and the latest sign that the general election has now begun in earnest.

The new ad, which begins airing tonight in Colorado, Florida, Iowa, Nevada, Ohio and Virginia, seeks to link Romney to major oil companies.

“Mitt Romney stood with big oil...for their tax breaks...attacking higher mileage standards and renewables,” says the ad’s narrator.

Watch it here:

This is the second ad that Obama’s reelection campaign has run. Both commercials have a) focused on energy and b) responded to attacks being paid for by conservative aligned groups.

The first pushed back against commercials funded by Americans for Prosperity, the conservative group funded by the Koch brothers, that attacked Obama for his ties to a failed energy company named Solyndra. That ad castigated “secretive oil billionaires” for unfair attacks.

This ad is in response to a commercial funded by the American Energy Alliance , which is running ads hammering Obama on the price of gas. (The AEA also has some ties to the Kochs.)

What does the new Obama ad tell us about his campaign strategy? A few things.

First, the Obama team clearly believes the general election is now underway. Naming Romney in an ad amounts to dropping the green flag on the fall campaign. acknowledging that whether or not Romney has the delegates to formally be the nominee that he is going to be the GOP choice.

“It’s no surprise President Obama is spending his soon-to-be $1 billion war chest to attack Mitt Romney and deflect blame for his failure to control gas prices,” said Romney campaign spokeswoman Andrea Saul.

Second, the fact that Obama has now run two ads on energy — both of which hit the oil industry — suggests that the campaign sees “Big Oil” as a major bogeyman to exploit over the coming months.

Third, the focus on energy — and particularly Solyndra and gas prices — is evidence that the president’s team knows he has vulnerability on those issues and wants to shore him up (and tear Romney down) as much as possible as soon as possible.

Remember that television ads are a telling window into a campaign’s strategy. Hundreds of thousands — and often millions — of dollars are spent running them. And no campaign, not even one as flush as President Obama’s, drops that kind of cash without thinking carefully and critically about the message they are sending — and, as importantly, why.