Pat Toomey says he has "serious reservations" about Trump.
The survey was conducted after the second presidential debate of 2016.
The Texas Republican called Hillary Clinton "an absolute disaster."
The Senate leader asked a woman to stop recording a speech he gave in Kentucky.
Johnson is pledging to make his next term his last if he wins a tough reelection race in November.
But the Speaker also won't rescind his endorsement.
Cristina Marcos 10/08/16 06:16 AM EDT
The relationship between the two has been fraught with tension from the start.
The Senate Republican leader said the comments are "repugnant and unacceptable."
The bill reforms handling of sexual assault cases.
Portman blasted Reid for "petty partisan politics" over his first responders bill.