there isn’t really any way to force Republicans to speak to sustain a filibuster. The Senate can only proceed to a vote on a bill either by unanimous consent, or by getting 60 votes to invoke cloture. As long as one Republican is on the floor, all s/he has to do is object to any request for unanimous consent, and the Democrats have to get 60 votes. The threshold required for cloture is a percentage of sitting senators, not senators voting, so the Republicans wouldn’t even need to be there to vote against cloture; they just need to refrain from voting for it. The Democrats, on the other hand, would need to keep at least 50 members on hand at all times to respond to a quorum call, or else the Republican in the chamber would suggest the absence of a quorum and the Senate would adjourn. So Democrats would be bearing the brunt of whatever physical toll this would take, and Republicans would be the ones getting a good night’s sleep, and would have no incentive to cave. After all, Republicans are happy for the Senate to do nothing over the next two years; with Democrats in the majority, a long stalemate like this would be taking time away from work and votes on Democratic priorities, not Republican ones. The Republicans tried keeping the Senate in session continuously a few years ago to try to pressure Democrats to abandon some filibusters of judicial nominees, and it didn’t work. A similar effort in 2009 would encounter the same problems.
The only time a read-the-phone-book, wet-your-pants filibuster like in a Jimmy Stewart movie would take place would be when Democrats had the 60 votes to invoke cloture and Republicans could only stop them by refusing to relinquish the floor so that a vote could be called. Then McConnell really would have to keep talking. But this sort of filibuster never really happens, because it has no chance of working. After all, unless you’re actually in a Jimmy Stewart movie, the 60 person majority can keep being 60 people longer than any one person can stand and talk, so unless some Senator wants to get headlines for him or herself in a losing cause there isn’t any reason to do it.
I asked him why we have the interesting historical filibusters we do, like the one where Huey Long spent hours reading out his favorite recipes and how to make pot liquor, and he explained:
These are generally theatrical, rather than actual efforts to change the outcome. At best, the filibustering senator could hope to raise the profile of the issue, but he had no real hope of winning the vote. Long’s filibuster failed to stop the New Deal bill he was opposing, or to force the changes he wanted. Strom Thurmond’s record-setting filibuster similarly failed to stop the Civil Rights Act of 1957 (which had already been gutted by Richard Russell, anyway). The record he broke belonged to Wayne Morse, who also failed to stop the bill he was protesting against. All three were pretty assiduously self-promoting, even for senators, and they were hoping both to make their point in a dramatic way and to advance their own careers by doing so. And a lot more people remember them and their filibusters than the bills they were fighting, so I suppose it worked.