Hi Clark
Notice that,
remain doesn't have -
ed morphology, which would make it a participle, a nominal. Note also that, the modal
may cannot function as a verb. Which means that
remain is the verb.
There are three verb phrases:
Ex: That Republicans are still in charge, and [that they] may remain so after November, is due ... to Bill Clinton's ... .
The ellipsis is 'that they', giving the subject-verb pair here:
Ex:...and that they may remain ...
