I actually respect Corker and Flake more than I do McCain, when it comes to speaking out forcefully against Trump.
It took McCain to literally receive a death sentence to finally grow a set of balls (in other words, when he had nothing left to lose, he decided to seek redemption), while Corker and Flake could have had a continuing political career, but chose to walk away from that (for whatever reason), and speak out against Trump.
The same can be said for Senators Susan Collins and Lisa Murkowski – who demonstrated even bigger balls by opposing the healthcare repeal, and remain in office!