However, there may be reasons that EST senators would want a shutdown. If these senators give the Tea Party its desired shutdown, the likelihood of being primaried goes down. The EST senator may also have a better chance of winning the nomination, but may have a lower chance of winning in the final election.
Tea Party senators (TP) may actually increase their numbers if the establishment prevents their desired government shutdown. That would prompt more challenges to EST senators, more TP nominees, and maybe less voter backlash in the final election.
So, what strategy is better for each group? Damned if I know. Another important question is what calculation will drive the decisions of each senator. Will it be the greater good, what is most likely to ensure reelection, or what is most likely to give the Senate majority to the GOP? Damned if I know again.
Extra. More of my posts about the Senate.