After Mitt Romney won the first debate, President Obama’s campaign released video of MSNBC’s Andrea Mitchell citing the “nonpartisan Tax Policy Center” study that disputes Romney’s claims about his tax proposals. This TPC study provides the basis for Obama’s claim that Romney will raise taxes on the middle class.

How “nonpartisan” is the Tax Policy Center? It’s well-known that one of the co-directors of the study worked in the Obama White House, but the Obama team counters by noting that another co-director worked for President George H.W. Bush before Clinton defeated Bush.

But TPC is a joint-venture of two liberal organizations — the Brookings Institute and the Urban Institute. How liberal? FEC records show that individuals associated with the two groups — ranging from low-ranking staff to current Obama aides such as Gene Sperling, a Brookings Fellow when he donated to Rahm Emanuel’s 2001 House campaign — have donated hundreds of thousands of dollars to Democratic candidates and liberal political outfits.

FEC records show that donors who listed the Urban Institute as their employer have given over $81,000 in recent election cycles to Democratic and liberal groups. A similar review of records for donors who listed the Brookings Institute as an employer gave over $122,000 to liberals, compared to just $3,300 to Republicans candidates or conservative organizations.

Obama deputy campaign manager Stephanie Cutter admitted to CNN that the central claim of the Obama ad that features Mitchell and the Tax Policy Center is not true.