the repubs are being stubborn because this election is much more than the candidates themselves, it is about ideology and politics.  this is a very crucial election due to the appointment of 2-3 supreme court judges and with the repubs currently controlling the congress (though they may lose control of the senate), they will want to control the power by having control in the house, the presidency and supreme court and hopefully retain control in the senate.  so it is understandable that ryan and McConnell stead fastly support trump.  they don't like trump but that is their candidate vote for by the party members.