Why Are Some Bishops Saying You Can't Vote Democrat?

"In this statement, we bishops do not intend to tell Catholics for whom or against whom to vote. Our purpose is to help Catholics form their consciences in accordance with God's truth. We recognize that the responsibility to make choices in political life rests with each individual in light of a properly formed conscience, and that participation goes well beyond casting a vote in a particular election."

This quote is from "Forming Consciences for Faithful Citizenship" the official document of the U.S. Bishops.  http://www.usccb.org/issues-and-action/faithful-citizenship/

Read the document and compare to reports of some Bishops saying you can't vote for party "x" or candidate "y".

And listen to Pope Benedict

With regard to voting for a pro-choice candidate Cardinal Ratzinger (now Pope Benedict XVI) stated: "When a Catholic does not share a candidate's stand in favor of abortion and/or euthanasia, but votes for a candidate for other reasons, it is considered remote material cooperation, which can be permitted in the presence of proportionate reasons." (Ratzinger-Memorandum July 6, 2004)  http://www.catholicsforcommongood.org/election.htm