President Obama's budget proposal is important as a statement of priorities and a marker in the debate over discretionary spending that's just getting underway in Congress. But it also misses the big picture. As Kevin Drum and my colleague Jonathan Chait note today, social insurance programs (Medicare, Medicaid, Social Security) and defense spending account for nearly two-thirds of all federal spending. Throw in interest on the debt and you're up to three quarters.

To quote Ezra Klein, who's also posted the graph above, the federal government is basically an "insurance conglomerate protected by a large, standing army." And none of the spending proposals we're talking about right now substantially affect these expenditures, save for some tinkering in Medicare and the Pentagon budget.

Of course, the Obama Administration and its allies did attempt to work on controlling those portions of the budget, by enacting health care reform. And the Affordable Care Act actually makes some progress, albeit not enough. But their opponents (i.e., the Republicans and their allies) attacked them mercilessly for it, which is why Obama's latest budget attempts no further adjustments--and why, for now, a more serious conversation about long-term fiscal balance is not taking place.