Conservatives have long attacked the Buffett rule as an example of an Obama "class warfare" mind-set. Their argument is essentially that low tax rates for all Americans will help the whole economy prosper.
Obama sought to fight back on that front Tuesday.
"This is not simply an issue of redistributing wealth," he said. "This is not just about fairness. This is also about growth. This is also about being able to make the investments we need to succeed."
You can expect this philosophical debate between Obama and Republicans to be a loud and long one between now and the November election.
Conservative economists say that low tax rates on business and on capital gains help spur job growth. They note that many small businesses pay their taxes by way of the owner's personal income tax return, so a tax on millionaires is also a tax on job creators. They add that marginal tax rates on top earners would go much higher than 30 percent under a Buffett rule, when you account for factors like state taxes and the way the Buffett rule's phase-in would affect incomes between the $1 million and $2 million level.
Republicans argue, moreover, that the Buffett rule could be the tip of a tax iceberg. They say many congressional Democrats would like to raise taxes on the middle class, not just on the rich, rather than impose spending discipline during a second Obama term.
Obama contends that the Buffett rule won't be onerous, that he has a track record of cutting taxes on small businesses, and that US prosperity depends on taking prudent steps to close federal deficits and sustain the middle class. He accused Republicans of wanting "to double down" on a failed strategy of cutting taxes for the very rich.
"In America, prosperity has never just trickled down from a wealthy few," Obama said. "Prosperity has always been built from the bottom up, and from the heart of the middle class outward."