If you want to know how President Obama plans to campaign this fall against likely challenger Mitt Romney, you need only check out his Saturday radio address. The key moment was when he renewed his populist pitch to raise taxes on rick folks' investment income.

While lamenting the fact that the rich who rely on investment income pay taxes at a much lower rate than wage-earning and salaried working stiffs, Obama again urged Congress to enact a law requiring that the rich be taxed at a 30 percent rate (good luck with that idea). Here was his key passage:

"Some people call this class warfare. But I think asking a billionaire to pay at least the same tax rate as his secretary is just common sense. We don’t envy success in this country. We aspire to it. But we also believe that anyone who does well for themselves should do their fair share in return, so that more people have the opportunity to get ahead – not just a few."

That sounded on the surface like a policy riff, but, rest assured, it was actually raw politics. And it was aimed squarely at Romney.

Congress rarely does anything substantive in a presidential election year, and the current partisan divide between House and Senate makes it even more improbable. Obama knows there isn't the remotest chance that his proposed tax hike on the wealthy will wind up on his desk for a signature. The pending Senate bill - nicknamed "the Buffett rule," a reference to investor Warren Buffett, who says that he's taxed at a lower rate than his secretary - is slated for a vote on April 16, but it's all about political positioning.

Obama knows the GOP lawmakers will stay in character and service their top-bracket masters by blocking the bill. Indeed, Republicans already insist that the Buffett rule would reap only $47 billion in revenue over the next 10 years – predictanbly omitting the fact that this projection (by a congressional tax panel) is pegged to the assumption that George W. Bush’s tax cuts for the rich will expire on schedule and flood Uncle Sam's coffers with far higher amounts of revenue.

The hitch, of course, is that the GOP has no intention of allowing the Bush tax cuts to expire on schedule. If the Bush tax cuts remain in place, the Buffett rule would be one of the only mechanisms for greater fairness. The Tax Policy Center, a Washington think tank, estimates that the Buffett rule, absent the Bush tax cuts, would reap hundreds of billions in new revenue.

But, of course, the GOP will block the Buffett rule  as well. And when they do, Obama will have a campaign issue to drape around Romney's neck. As he said in his radio address, "Every member of Congress is going to go on record. And if they vote to keep giving tax breaks to people like me - tax breaks our country can't afford - then they're going to have to explain (themselves)."

A cynical tactic on Obama's part? Absolutely. But that's how the game has long been played in election years. His naive faith in bipartisan cooperation has been expunged. The priority now is to frame the dialogue by defining the opposition party - and the candidate who's likely to lead that party.

Which brings us to the first passage I quoted, the one where Obama says that "anyone who does well for themselves should do their fair share in return." That's all about Romney, who made $42 million in investment income during the past two years, with the feds taking only 15 percent thanks to an unjust tax code that's heavily tilted toward people like him.

So Team Obama's autumn strategy is to stump for "fairness" - in his radio address, Obama said the Buffett rule would "make this country a little fairer" - while painting Romney as the personification of unfairness.

Buffett himself says that Romney "makes money by moving around big bucks, not by straining his back or going to work and cleaning toilets or whatever it may be." And Romney seems determined to help Obama own the fairness theme, as evidenced by the news that the lavish renovations on his coastal California manse include plans for a special elevator that will move his cars between floors.

Yes, the Buffett rule, as legislation, is surely dead on arrival. Which is why, as a campaign issue, it lives. When Romney grudgingly released his tax returns back in January, he said that the 15 percent tax rate on his investment income was "fair....absolutely."  That’s a debate Obama would look forward to having.

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Would Obama take a big political hit this fall if the high court turns thumbs-down on Obamacare in June? Not necessarily. My Sunday newpaper column, here.

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