In this case the problem was Paul Ryan and congressional procedure which Ryan could have fixed by polling the house. McCain said he would vote for the measure just to advance it to the next step which would be a House Senate conference committee. He did not want the house to just pass the Senate bill and send it to Trump. Therefore, he asked Ryan to pledge that this would not happen (even if it meant polling the House that night). Ryan would not do this and just said he was willing to ask the House to discuss the bill with the Senate-- leaving it open to pass the bill and send it to Trump. Another problem resulting from rushing things, mistrust, and secrecy in the Republicans' procedure. Plus lack of leadership by Ryan and McConnell who should have dealt with this (they could have sought a commitment from Trump not to sign the bill until it went to the conference committee).