"the real reason that the RNC and some big money donors don't want Trump
as President to win the Republican nomination" (FTFY) ... is because if he does, Hillary wins by a landslide, Republicans will be purged from currently-held Congress and the Senate, and their party all but destroyed by bitter infighting.
Some of the biggest 'traditional' Republican donors (e.g. Koch bros) are already making noises about switching their support to Hillary.
So if you want another 'Republican Lite', elect another Clinton.
If Cruz gets the nomination, Hillary wins by a landslide but the Republican Party will survive in a weakened state to fight another election (maybe), with Tea Party nutters (like Cruz) a discredited, spent force.
EDITED: 26 Apr 2016 15:08 by DSMITHHFX