Bruce A. Dixon, of Black Agenda Report, in an article about Newark Mayor Corey Booker, and what his success as a politician means for black political issues:
The right has decisively invaded the politics of black America, and owns the Democratic party outright. Barack Obama is effectively a center-right president, pursuing wars, prosecuting whistleblowers, shielding banksters, and using cruise missiles to dispatch suspected terrorists with an impunity the Bush-Cheney gang never enjoyed With black Democrats routinely shilling for imperial wars, austerity, school closings, privatizations, bailouts and kindly treatment for their campaign contributors, there are no outlets in the two parties for the real needs and desires of much of black America. The two party system has become people-proof and democracy-proof.
Corey Booker and the Hard Right's Colonization of Black American Politics
I think you could do a global substitution of "progressive" for "black" in that paragraph, and it would still be largely true. While it's likely that how things played out worked differently, there's no doubt that conservatives, largely via the Democratic Party, call the tune pretty much everywhere.
Having explained why often enough that I don't feel the need to repeat myself, I'll just say that what this means to me is that the real problem is that both black and progressive politics became too much about Democratic politics, and at some point failed to be about what really matters. As long as major progressive organizations continue to depend on the Democratic Party for funding, as some like Media Matters and the Center For American Progress do, that will continue to be a problem.
The National Rifle Association, LGBTs, and Wall Street have all shown that the way to influence politics isn't to be slavishly loyal to one party. It's to make it perfectly clear that their support can go elsewhere.
When progressives learn to do that, politicians may take them seriously. They certainly won't until then.