I have yet to hear an actually compelling reason for him to recuse himself.
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Dems don’t think they need an actual reason after Sessions caved at the first hint of criticism. If Nunes goes soft, the Dems will next be asking for the entire GOP caucus to resign, so they can take the govt by default.
Sessions had to recuse himself for a simple reason: Being a part of the campaign team means that if there is an investigation of the campaign, he would have to recuse himself.
What he did was completely appropriate and standard.
What they are arguing in this case is, well, stupid.