I have blogged about this since time immemorial, but if you need primers on what, precisely, the Church teaches about Catholics and the political life, go here:
There are links to several USCCB docs, statements by (former) Archbishop Cardinal McCarrick of DC, and things from America magazine, although I generally hold that publication at arm's length due to some of the comments of its editors on TV.
Trinity College, btw, is Nancy Pelosi's alma mater. Methinks she should read the President's blog. But I really doubt she cares. Much like John Kerry.