Social Security Reversal in Md. Senate Race: Six Lessons For Democrats

3. The public has a long memory -- and needs commitment from its candidates.

Rep. Van Hollen's public advocacy of Simpson-Bowles reached its height in 2012, but he's being forced to defend himself for it three years later. Three years is a long time in political cycles.

When the political mood shifts, the public doesn't necessarily forget. That's why it was wise for Rep. Van Hollen to support Social Security expansion. But it's also why he needs to do more: The public has grown used to seeing politicians express support for a program at election time, only to offer it up for sacrifice later.

Sure, politicians must sometimes compromise. But the public needs to know that some programs are off-limits -- especially today, with extremist Republicans riding herd over their party. That's why groups like MoveOn.org and CREDO have called upon Rep. Van Hollen to state unequivocally that he will not support Social Security cuts in the future. Better to have no budget deal at all than to have one that extracts a lifetime's worth of sacrifice from America's seniors.

As CREDO political director Becky Bond said recently, "Van Hollen needs to draw a line in the sand and make it clear that he will vote against any bill that cuts Social Security or Medicare benefits."

4. Progressive politicians are changing the debate.

It is unlikely that Rep. Van Hollen would have shifted his position on Social Security if Rep. Edwards had not challenged him. Edwards represents the American tradition of independently minded progressive leaders -- leaders like Massachusetts Sen. Elizabeth Warren, Reps. Keith Ellison (Minn.) and Raul Grijalva (Ariz.) of the Congressional Progressive Caucus, Sen. Bernie Sanders, Florida Rep. Alan Grayson, Ohio Sen. Sherrod Brown, and a number of other courageous officials.

The political discourse won't change unless party hierarchies and artificially imposed "consensus thinking" is challenged by leaders such as these. The inverse is also true: Leaders like these can, and do, make a difference.

5. Independent activism is critical.

This shift in Maryland's race can also be attributed to the hard work of independent activists. Issues-based groups have played an essential role in shifting the public debate. Other independent organizations are moving the "Overton window" through other means -- by researching the issues, promoting issues-related activism, and/or supporting progressive political candidates.

6. Hillary Clinton and other national candidates face an opportunity -- and a risk.

Politicians should remember: voters don't forget. The Beltway's "bipartisan" agenda is fundamentally unpopular, and those who promote it may have to defend their actions in the years to come.

While Hillary Clinton has yet to state her position on many key economic issues, President Clinton and a number of Clinton team members are closely associated with Simpson-Bowles and other unpopular "centrist" ideas.

The mood among the Clinton team seems to have shifted, at least somewhat, in recent months. Clinton associates and advisers are increasingly discussing wealth inequality and other populist-related issues. The (presumptive) candidate herself has also raised these themes in recent comments.

But voters have been burned, and are increasingly skeptical of promises that lack the force of commitment. They've heard progressive rhetoric from presidential candidates, only to see those candidates reverse themselves upon attaining the presidency. (There's a plausible argument to be made that Bill Clinton, as well as Barack Obama, ran considerably more progressive campaigns than was later assumed in the "conventional wisdom.")

Voters are likely to remain dubious about candidates who offer only vague platitudes about key issues like jobs, wages, and trade, without making firm commitments or offering specific proposals. The Maryland race has just begun, of course. But so far, it seems to point to the pitfalls of corporate "centrism" -- and the promise of economic populism.