McCain chairs a committee right? He could call for an investigation on his own if I'm not mistaken.
He chairs the Armed Services Committee, which currently has a 14-12 Republican majority. Graham is also on the committee, so in principle if McCain and Graham joined the Democrats in a vote on that committee, they'd have a majority.
Of course, that's in *this* Congress. I suppose if McConnell was really worried about McCain going rogue, he could try to strip McCain's chairmanship in the next Congress, but that would obviously be a rather controversial move.
