In a letter to their Democratic...

...colleagues, Sen. Patty Murray, chairwoman of the Budget Committee, and Sen. Max Baucus, chairman of the Finance Committee, state (my emphasis):

President Obama has been clear that he is not going to negotiate over the debt limit, and Congressional Democrats stand behind him strongly.

Since 1960, the debt limit has been raised a total of 78 times, including 49 increases under Republican Presidents and 29 increases under Democratic Presidents. President Ronald Reagan said in 1983 that, "the full consequences of a default -- or even the serious prospect of default -- by the United States are impossible to predict and awesome to contemplate."