Sen. John McCain (R-AZ) was diagnosed with brain cancer following a surgery to remove a two-inch blood clot from above his left eye. Amateur president Donald Trump has failed to deliver a message on his always-busy Twitter timeline, but former President Barack Obama did to show solidarity with the 80-year-old Senator. It is, after all, not a partisan issue to show you have a person s back when they need it most. To show that politics doesn t have to be bitter when someone s life might be on the line. Obama and McCain go way back to his first election. When a woman in the audience at a rally called Obama an  Arab,  McCain shut her down. In contrast, Donald Trump launched the birther conspiracy theory in order to delegitimize our country s first black president.President Obama tweeted,  John McCain is an American hero & one of the bravest fighters I ve ever known. Cancer doesn t know what it s up against. Give it hell, John. John McCain is an American hero & one of the bravest fighters I've ever known. Cancer doesn't know what it's up against. Give it hell, John.  Barack Obama (@BarackObama) July 20, 2017Obama s tweet has gone viral with over 373,000 likes so far. In 2015, Trump crossed the line with McCain, going where no person should go. He s not a war hero,  Trump said of McCain.  He was a war hero because he was captured. I like people who weren t captured. McCain, a former Navy pilot, spent approximately five-and-half years in a notorious North Vietnamese prison known as the  Hanoi Hilton,  where he was repeatedly tortured. John McCain spent two of those years in solitary confinement.Unfortunately, Donald Trump hasn t mentioned McCain s health yet. The former reality show star failed to contact former President Jimmy Carter after he collapsed on Thursday while working on a Habitat for Humanity home in Winnipeg, Canada. Prime Minister Justin Trudeau did call Carter, though, to wish him well. That s what leaders do. They lead by example.Photo by Alex Wong/Getty Images.