Which part?
The mortgage collapse was due to government social policy overriding good fiscal sense, and a lot of greedy bankers who were more than happy to have the government as a working partner in what should never have been a government operation.
Our massive entitlement debts have mostly liberal fingerprints all over them, over many decades. Mostly: unfortunately Bush also passed a new Medicare entitlement. It's small comfort that the Democrats wanted a bigger one.
The Democrats have owned the House and Senate since January of 2007.