Rejecting the party line
The US Senate building in Washington, DC.
Senate votes are almost never surprising, especially during hyper partisan times when everybody votes along party lines.
But decisions to defect may be based on more than idealism. Indeed, the likelihood that someone strays from their party may even depend on the spelling of their last name, according to a paper in the July issue of the American Economic Review.
They say that US Senators whose last names positioned them to vote earlier were more likely to go against their party than those who voted towards the end.
Figure 1 from Spenkuch et al. (2018)
The figure above shows that this pattern is particularly pronounced in close votes. When bills appeared headed for easy passage, Senators who voted first were not that much different from those at the end.
It’s worth noting that this effect didn’t happen in the House, where alphabetic roll calls became obsolete after the introduction of electronic voting machines.
Senators who defect early in the process may be taking advantage of their position to cast a more favorable vote knowing that their peers at the end of the roll-call will toe the party line and deliver a victory so they don’t have to.