President Obama, at an event just now promoting the Buffett Rule:

If we’re going to keep giving somebody like me, or some of the people in this room, tax breaks that we don’t need and can’t afford, then one of two things happens. Either you’ve got to borrow more money to pay down a deeper deficit, or you’ve got to demand deeper sacrifices from the middle class, and you’ve got to cut investments that help us grow as an economy.

You’ve got to tell seniors to pay a little more for their Medicare. You’ve got to tell the college student, `We’re gonna have to charge higher interest rates on your student loan, or you’re going to get smaller student loans.’ You're going to have to tell that working family that’s scraping by that they’re going to have to do more because the wealthiest of Americans are doing less. And that’s not right. The middle class has seen enough of its security erode over the last few decades. And we shouldn’t let that happen.

We’re not going to stop investing in the things that create real and lasting growth in this country, just so folks like me can get an additional tax cut. We’re not going to stop building first class schools and making sure that they’ve got science labs in them. We’re not going to fail to make investments in basic science and research that could cure diseases that harm people or create the new technology that ends up creating entire industries that we haven’t seen before.

Obama’s case for reeection may hinge on whether he can convincingly make the case that his push to combat inequality and tax unfairness isn’t just about basic morality, but also about promoting economic growth and broader prosperity. Republicans are laying the groundwork to paint Obama’s push on taxes as an effort to distract from his failed economic record by diverting public anger about the economy towards the rich. That is to say, they are looking to separate the debate over taxes (where Obama seems to have the upper hand) from the debate over the economy (where they hope to put Obama on the defensive). When Romney argues that government shouldn’t try to address inequality by redistributing wealth, but by freeing up the private sector to promote opportunity and social mobility, he’s also trying to achieve this separation.

Obama’s challenge is to argue that combatting inequality and tax fairness are all about promoting opportunity and mobility — that the two are connected, and that the Republican argument is premised on a false choice between the two. He will argue that addressing those inequities is the only way to ensure that government can continue investing in the country’s economic future and in shoring up the middle class.

As the New York Times editorial board puts it, the “discussion of inequality must not end with a debate on taxes.” Obama needs to make a broader pitch for government to “do a lot more to strengthen the institutions that foster broad prosperity,” such as public education, financial regulations, and universal health care. Obama took a step in this direction today.

His case isn’t an easy one to make, given public skepticism about the stimulus and about government’s ability to create jobs. But his argument could get an assist from the fact that Romney’s vision, too, will be placed before the voters — reminding Americans what happened the last time a GOP president promised that shrinking government and cutting taxes for the rich were the best routes to job growth and shared prosperity.