Doesn’t Pat Roberts want a debate on immigration?

It was disappointing that Sen. Pat Roberts, R-Kan., voted against allowing debate on a bipartisan immigration reform bill – one of only 15 senators (all Republican) to support a filibuster. Doesn’t he think the Senate – supposedly the world’s greatest deliberative body – should debate and vote on the reform? Or is this another case of Roberts moving further to the right in order to ward off a GOP primary challenge next year?