Below we use Optimal Classification (OC) in R to plot the Senate’s 54-41 vote to prohibit funds from being used to transfer detainees from Guantanamo Bay and its 61-38 vote to ratify a United Nations treaty to prohibit discrimination against disabled persons. Because a 2/3 vote is required for Senate ratification, the treaty was rejected. The Guantanamo Bay amendment was sponsored by Sen. Kelly Ayotte (R-NH), who is considered to be a rising star in the Republican Party (particularly on foreign policy issues).
Both votes attracted a considerable number of partisan crossovers: 10 Senate Democrats supported the ban on transfers from Guantanamo Bay, and 8 Senate Republicans voted to ratify the UN treaty for disabled rights. The plots below show the power of the spatial (geometric) model of choice in correctly classifying most of these Senators who broke ranks with their party based on their liberal-conservative position. Most of the crossover Democrats and Republicans are in the moderate wings of their parties. For example, Democrats who voted “Yea” on the Guantanamo Bay included Senators Joe Manchin (D-WV) and Ben Nelson (D-NE), and Republicans who supported ratification of the UN Treaty included Scott Brown (R-MA), Susan Collins (R-ME), and Olympia Snowe (R-ME).
However, the vote on the UN Treaty for Disabled Rights also featured limited conservative support (e.g., Senators John Barrasso (R-WY) and John McCain (R-AZ) both voted “Yea”). Opposition to ratification centered around concerns that it would threaten US sovereignty, specifically on issues related to parental rights. Not all conservatives shared these concerns, but there were still only four classification errors on the UN Treaty vote, and only one on the Guantanamo Bay vote.