If, as franksolich says, the harder the administration appears to be hitting on Nelson, the more Nebraskans get behind him, then it would appear that it is, in fact, Nelson who benefits the most from being seen to be being browbeaten by the administration on something we all know they simply cannot do, which would in turn have the effect of protecting Nelson's seat from challenge.
It also gives him cover if he ends up casting a "yes" vote for whatever further monstrosity they dream up now - he can always say, "well, I didn't have much of a choice; we would have lost our base if I hadn't ultimately voted for it, but in my defense, I did make them make a lot of changes to it before I agreed to vote for it."
Just a thought.
For just a "thought," a good thought.
The problem Republicans in Nebraska have, when running against Nelson, is that he at times shows an independent streak, an anti-establishment streak (the "establishment" of course being the Democrats and entrenched bureaucrats in Washington), making it difficult for the average Republican voters to not support him.
Nebraska is a red state, but something else trumps that; as with the late George Norris, Ben Nelson is a burr in the saddle of the establishment, reminding them that Nebraska exists, Nebraska counts, and that it might be a pretty good idea to pay attention to Nebraska.
Thus far, two top-notch Republican candidates have run against Ben Nelson; high quality people, but obviously Nebraskans didn't think they could kick the establishment's ass as well as Nelson has, and Nebraskans most of all want the powers that be kicked around.