INVOKING THE SPIRIT of Teddy Roosevelt, President Obama traveled to Osawatomie, Kan., on Tuesday to underscore two related problems plaguing America: growing income inequality and mounting strains on many of the poor and middle class.

Although it prompted the inevitable accusations about class warfare, Mr. Obama’s focus on income inequality is justified. “The rungs on the ladder of opportunity,” as he said, “have grown farther and farther apart.” A new report by the Organization for Economic Cooperation and Development (OECD) makes clear that the gap between rich and poor is growing throughout the industrialized world.

Republicans who deny the phenomenon or its ill effects would do well to recall the admonition of Mr. Obama’s predecessor. “We have an obligation to help ensure that every citizen shares in this country’s future,” George W. Bush said in 2007. “The fact is that income inequality is real. . . . And the question is whether we respond to the income inequality we see with policies that help lift people up or tear others down. The key to rising in this economy is skills, and the government’s job is to make sure we have an education system that delivers them.” That is closer in spirit to Mr. Obama’s message in Kansas than to the anti-government rhetoric of this year’s Republican candidates.

Mitt Romney, for example, on Wednesday inaccurately accused Mr. Obama of “seeking to replace our merit-based society with an entitlement society” in which “everyone receives about the same rewards.” Mr. Romney asserted that as entrepreneurs “exert the effort, and take the risks inherent in inventing and creating things, they employ and lift the rest of us, creating prosperity for all of us. The rewards they earn don’t make the rest of us poorer — they make us all better off.” Mr. Romney is right that economic growth is essential. But evidence suggests that even a rising tide may no longer lift all boats, without new policy approaches.

That leads to one weakness in Mr. Obama’s speech: His policy prescriptions, at least so far, don’t match the gravity of the problem he describes. In addition, to the extent he finds villains in American corporate greed or weak regulation, he misses the OECD’s point that the phenomenon, fueled in large measure by globalization and new technology, transcends borders and political systems.

Of most concern is what the president omitted or played down. He made glancing reference to the need to “get our fiscal house in order” and immediately pivoted to the imperative of extending the payroll tax holiday. The economic growth that will be essential cannot happen with the dampening overhang of ever-mounting debt. Nor can the spending Mr. Obama rightly prescribes for education, research and infrastructure.

The president is right that the Bush tax cuts for the wealthiest Americans are unwise and unaffordable, but ending them won’t be enough. Carving out the fiscal space to make the needed investments will require far more than simply going after millionaires and billionaires. To quote the president, “That is not politics. That’s just math.”