It feels as though every time I've looked at voting records from the U.S. congress, I notice that virtually everyone votes with their party; that is, for any given bill, every Republican votes the same as every other Republican, and every Democrat likewise votes the same as every other Democrat. The number of exceptions tends to be very low - typically less than ten from either party, which is a tiny amountnumber of the House of Representatives' several-hundred members. Further, it seems the more consequential the vote, the more likely for members of congress to vote with their party, rather than against.
Have there been any studies of the historical strength of this trend? I.e., how the number of "rogue" votes in either house has changed over the years? Is this tendency of parties to vote en bloc a (relatively) recent phenomenon, or has it been the trend for as long as the U.S.A. has had political parties?
PLEASE NOTE: I am not asking about the reasons, mechanisms, ethics, or anything else related to the practice of "voting the party line" in the U.S. I am only interested in the history of the practice with this question. The moral implications of it are an entirely different discussion for some other time.
