President Obama has again acknowledged the necessity of doing something many Democrats fiercely oppose -- reforming entitlement programs, such as Medicare and Social Security.

On a Midwest bus tour stop in Minnesota, Obama spoke in favor of changes to entitlement programs being eyed by the 12-member congressional committee charged with finding budget savings that will get past partisan gridlock, stave off future credit downgrades and increase the federal debt limit by $1.5 trillion.

"There have been times when our side, when Democrats aren’t always as flexible as we need to be," Obama said. "Sometimes I do get frustrated when I hear folks say, 'You can't make any changes to any government programs.' Well, that can't be right."

The president has repeatedly conceded that something must be done, saying Medicare in particular cannot survive without reform.

"We will not be able to sustain that program no matter how much taxes go up," he said in late July. "I mean, it's not an option for us to just sit by and do nothing."

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In spite of that, just as the president suggested, many Democrats remain steadfastly opposed to any changes in any of the programs. In fact, House Democratic leader Nancy Pelosi boasted that Democrats had blocked such reforms in the deficit talks.

"We did protect the benefits, the Social Security, Medicare and Medicaid benefits. That is a priority for us," she said.

David Walker is the former head of the General Accounting Office and now head of the Comeback America Initiative. He suggests the entitlement programs are promises the government can’t pay for.

"Government has a tendency to overpromise and underfund," he said. "And the fact of the matter is, if you have an unfunded promise, it's a false promise."

Officials at the credit rating firm Standard & Poor’s, which recently downgraded the debt of the federal government, also point to soaring entitlement costs as a key reason for its action.

"Entitlement reform is important because entitlements ... are the biggest component of spending, and they are the part of spending where the cost pressures are greatest," David Beers of S&P said.

And budget analysts couldn't agree more.

"We need to focus on the real problem parts of the budget,” said Maya MacGuineas, president of the non-partisan Committee for a Responsible Federal Budget. “That's Medicare, Medicaid and Social Security."

Medicare and Social Security taken together have promised $46 trillion more in benefits than the government has a plan to pay for.

"That's how much money you'd have to have today, invested at treasury rates, in order to close the gap between the revenue that we have and expenditures that we are expected to have," Walker said.

Yet many on the left say entitlements must not be cut.

"By all means, there should be no cuts in Medicare and Social Security and Medicaid in this process," said Robert Borosage, head of the liberal interest group Campaign for America's Future.

But analysts argue that simply will not work.

"We're not going to fix this problem without fixing entitlements," MacGuineas said. "Social Security, Medicare, Medicaid are at the center of our fiscal challenges."

In fact, 60 percent of all federal spending is now for entitlement programs.