President Obama and his political counselors do not appear to recognize or respect the depth of the disenchantment among Democrats who fear he is preparing to abandon the commitments made by Franklin Roosevelt, Harry Truman, John Kennedy, Lyndon Johnson and generations of Democratic leaders to not just preserve but expand Medicare, Medicaid and Social Security.

At a recent gatherings with liberal Democrats and progressive independents in Massachusetts, Pennsylvania, Minnesota, Wisconsin and Obama’s home state of Illinois, I have been struck by the extent of the frustration with the president. There has always been a good deal of griping about Obama’s maintenance of the Bush administration’s wars in Iraq and Afghanistan—and his decision to launch a new fight with Libya—as well as compromises on issues ranging from health-care reform to regulation of Wall Street, but this is different. As Obama has seemed to weaken in his commitment to preserve Medicare, Medicaid and Social Security, anger with the president has become dramatically more widespread.

A new CNN/ORC International Poll confirms the phenomenon. The number of Americans who say they disapprove of the president’s performance because he is not liberal enough has doubled since May. “Drill down into that number and you’ll see signs of a stirring discontent on the left,” says CNN Polling Director Keating Holland, who explains that, “Obama’s approval rating among liberals has dropped to the lowest point in his presidency, and roughly one in four Americans who disapprove of him say they feel that way because he has not been liberal enough, a new high for that measure.”

The number of Democrats who say Obama should face a primary challenge in 2012 is growing, with almost a quarter of party backers surveyed by CNN refusing to say they thought the president should be renominated.

Vermont Senator Bernie Sanders, an independent who caucuses with Senate Democrats, gave voice to that sentiment Friday during a regular appearance on Thom Hartmann’s popular national radio show. When a caller who expressed frustration with Obama’s apparent willingness to accept cuts in Social Security, Medicare and Medicaid, Sanders said: “Discouragement is not an option. I think it would be a good idea if President Obama faced some primary opposition.”

Sanders explained: “Let me just suggest this: I think there are millions of Americans who are deeply disappointed in the president, who believe that with regard to Social Security and other things, he said one thing as a candidate and is doing something very much else as a president—who cannot believe how weak he has been for whatever reason in negotiating with Republicans, and there’s deep disappointment. So my suggestion is: I think one of the reasons the president has made the move so far to the right is that there is no primary opposition to him and I think it would do this country a good deal of service if people started thinking about candidates out there to begin contrasting a progressive agenda as opposed to what Obama believes he’s doing.”

Sanders says Obama’s weak approach to negotiations with Republicans with regard to Social Security, Medicare, Medicaid and tax cuts for the rich has caused him to “give thought” to encouraging a progressive Democrat to mount such a challenge.

That led to immediate talk about the prospect that Sanders might mount a primary challenge. That won’t happen. Sanders is not a Democrat. Besides, he is busy running for reelection in Vermont in 2012.

When Sanders said in March that “if a progressive Democrat wants to run, I think it would enliven the debate, raise some issues,” he explained that: “I’ve been asked whether I am going to do that. I’m not. I don’t know who is, but in a democracy, it’s not a bad idea to have different voices out there.”

No other “name” Democrat has, so far, engaged in a public discussion about making a primary run against the president.

There is some organizing on the ground among Democrats who would, at the very least, like to use Democratic caucuses and primaries to send a message to Obama. Antiwar Democrats in Iowa have talked up the prospect of a challenge in the state where the Democratic nominating process begins with caucuses that attract the party’s most activist base. There have also been stirrings in the District of Columbia, where resentment over Obama’s failure to defend the interests of the nation’s capitol is voiced.

But those initiatives aim more toward getting the president’s attention and shaking up a complacent national party, perhaps by asking caucus and primary voters to send uncommitted delegates—as opposed to committed Obama backers—to next year’s Democratic National Convention. Uncommitted delegates, at the least, could generate platform fights and pressure the president’s team on particular issues.

Even this project could be a tough one, however, as the nominating process is largely controlled by Obama operatives, who have already been working the schedule and putting in place structural supports for the president’s reelection run. Obama’s team is looking at the caucuses and primaries as tools to build enthusiasm for the president’s fall reelection campaign against the Republican nominee.

But if they are serious about that fall campaign, they are going to need to recognize and respond to the disenchantment among Democratic activists whose enthusiasm level will decide the fate of Obama’s 2012 campaign. Even if there is no primary challenge, Obama must reconnect with liberal Democrats and progressive independents if he hopes to be reelected. And he will not do so by cutting a deal with Republicans to cut Democratic “legacy programs” such as Medicare, Medicaid and Social Security.