Informal influences on legislators

Recently, I've been plugging my seating paper, in which I find that California legislators sitting next to each other can influence each others' votes.  Well, in their working paper "Friends in High Places," Lauren Cohen and Christopher Malloy take this a step or two further and find a similar effect in the U.S. Senate.  Senators sitting near each other, they find, tend to vote similarly.  (I'm not sure to what degree freshman senators get to pick their seats, so there may be some endogeneity issues there, but still an interesting finding.) They also find that college alumni networks help explain voting patterns among senators.