They have known this for years, long before he ever became their Presidential candidate. They only have themselves to blame for the damage done.
In 2004 before the presidential election, a family member who is staunchly democrat was telling me that if we stayed in Iraq my grandchildren would be serving there. (don't agree but anyway) ... I told this person that Bush might not be perfect, but Kerry was a TERRIBLE candidate. He agreed. :-)
But what could they have done? Muzzle him? He's a megalomaniacal elitist twit who is essentially unimpressed by what anybody thinks because he doesn't believe anybody to be capable of such an activity but him and his fellow elitists. They couldn't possibly have stopped him.