Following the news that US Senator for Arizona, John McCain, has been diagnosed with brain cancer, politicians from both sides of the administration stepped up to voice their support for the Vietnam War veteran.

The 80-year-old recently underwent a brain craniotomy to remove a blood clot above his eye.

The clot was then sent for pathology testing and was discovered to be associated with a primary brain tumour known as a glioblastoma.

"Thank all of you for the wonderful thoughts. @senjohnmccain is doing well. We as a family will face the next hurdle together," his wife Cindy McCain wrote on social media on 19 July (Wednesday) alongside a photo of the couple on their wedding day.

"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."

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.

A post shared by Cindy McCain (@cindymccain) on

His daughter Meghan McCain also shared a heartfelt note on Twitter, describing her father as "the toughest person I know".

"The cruellest enemy could not break him. 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. Nothing ever has," the 32-year-old Fox News host wrote.

"He is a warrior at dusk. One of the greatest Americans of our age. And the worthy heir to his father's and grandfather's name," she added. "But to me he is something more. He is my strength. My example. My refuge. My confidante. My teacher. My rock. My hero — My dad."

McCain survived the July 1967 fire and explosion on the USS Forrestal navy vessel that killed 134 sailors, the October 1967 shoot-down of his navy aircraft and fall into Truc Bach Lake in Hanoi, and five-and-a-half years in a North Vietnamese prison.

Politicians also took to social media, describing him as a "warrior" and "fighter", to express concern for the senator and send him their best wishes..