Now we learn that the Buffett tax the Senate is expected to vote on early next week will make the deficit worse. That’s because both Mr. Obama and Senate Democrats have made it clear that their new “fairness” tax is to offset the revenue loss from another provision related to the Alternative Minimum Tax.

That measure would exempt more than 20 million middle class Americans with incomes as low as $80,000 a year from getting nailed by the AMT. This year’s Obama budget clearly describes their intent: “The Buffett Rule should replace the Alternative Minimum Tax, which now burdens middle-class Americans rather than stopping the richest Americans from paying too little as was originally intended.”

The Joint Tax Committee—the official scoring referee on tax bills—calculates that the combination of AMT repeal for the middle class and the Buffett tax would add $793.3 billion to the debt over the next decade. As Mr. Obama has said, “This isn’t politics, this is math.”