Perhaps the most moving statements came from the senators daughter Meghan McCain and wife, Cindy McCain.
Meghan wrote of her father, He is the toughest person I know.
The cruelest enemy could not break him.
Credit: Paul Morigi/WireImage
The aggressions of political life could not bend him.
So he is meeting this challenge as he has every other.
Cancer may afflict him in many ways: But it will not make him surrender.
On Instagram, Cindy McCain added, Thank all of you for the wonderful thoughts.
@senjohnmccain is doing well.
We as a family will face the next hurdle together.
One thing I do know is he is the toughest person I know.
He is my hero and I love him with all my heart.
Give it hell, John.
Also wishing McCain well are several Hollywood stars, including Josh Gad, Alyssa Milano, and Marlee Matlin.
See their reactions and more below.
