In 2006, a Bush White House insider named David Kuo wrote in a tell all book that, "National Christian leaders received hugs and smiles in person and then were dismissed behind their backs and described as 'ridiculous' and 'out of control'." He asserted that Karl Rove and other senior political advisors regularly referred to evangelical Christians as "the nuts".
Two years after that those nuts, fed up with being taken for granted, became the tea party movement. And two years after that, the right of women to terminate their pregnancies is seriously diminished. Public education is undergoing withering budget cuts by a hoard of newly elected state legislators who favor church run schools. The government programs that freed people from relying on church communities -- with their near monopoly on social insurance -- are in the guillotine.
Progressives are a bit behind, but they are catching up fast. The evangelicals found out what their White House thought of them in 2006. Progressives found out the same in 2010 when Robert Gibbs groused aloud about "the professional left" and suggested that liberals are crazy and should be drug tested.
It took a few years to happen, but by 2009 the nuts were organized and in 2010 they took over the Republican Party. The "professional left," perhaps with the right as an organizational model, is moving forward faster.
Possibly as soon as next year, the left will be ready and able to stage serious primary challenges against Democrats that are seen as not supporting the principles Democrats arguably are supposed to support. Some of those challenges will result in moderate or conservative Democrats being replaced by liberal Democrats. Others will result in Republicans winning seats that more moderate Democrats might have kept.
The reality of this already has the fur flying in Democratic circles.
People who identify more closely with being Democrats than liberals or progressives are charging that principles have no value if there is no power to act on them. People who identify more closely with being liberals or progressives than with being Democrats are charging that power has no value if it isn't used to act on principles.
Since Bill Clinton ran as a "New Democrat", progressive principles have taken a back seat to power. If the left is successful, the result will be a much more progressive Democratic Party, a more polarized political atmosphere even than the one that exists today and, with luck, an under-represented moderate middle that will present a ripe opportunity for a strong centrist and, perhaps, a resurgance of the idea of negotiation and compromise that isn't totally one-sided.