The nonpartisan Congressional Budget Office puts it this way:

“With the population aging and health care costs per person likely to keep growing faster than the economy [gross domestic product], the United States cannot sustain the federal spending programs that are now in place with the federal taxes (as a share of GDP) that it has been accustomed to paying.”

Until Obama conspicuously and consistently acknowledges these realities in straightforward and unmistakable language — something he hasn’t done and shows no signs of doing — he cannot be said to be dealing honestly with the budget or with the American people. The main reason that we keep having these destructive and inconclusive budget confrontations is not simply that many Republicans have been intransigent on taxes. The larger cause is that Obama refuses to concede that Social Security, Medicare and Medicaid are driving future spending and deficits. So when Republicans make concessions on taxes (as they have), they get little in return. Naturally, this poisons the negotiating climate.

Of course, Obama would offend many Democrats if he entertained benefit cuts in Social Security and Medicare: higher eligibility ages, higher premiums for affluent elderly, structural changes in the health-care system to reduce costs.