I would offer two insights. First, sadly the abortion mentality is so pervasive in American culture; a devout, pro-life Catholic may not have a bona fide pro-life choice in elections. Second, moral theology teaches us that there is a difference between direct consequences (i.e. a Catholic cannot vote for someone with the intent of expanding or perpetuating abortion) and indirect consequences (this would be choosing the politician who, when no truly pro-life option is available, is the best on the gamut of issues encompassed by Catholic social teaching).
The Archdiocese of Milwaukee's "Living Our Faith" website has a Faithful Citizenship page with links to essays commissioned by the U.S. Bishops on a number of topics.