Republican Senator John McCain died in the early hours of Sunday morning at the age of 81.Former US president Barack Obama mourned McCain's passing in a statement published on his Twitter account. "John McCain and I were members of different generations... But we shared, for all our differences, a fidelity to something higher - the ideals for which generations of Americans and immigrants alike have fought, marched and sacrificed. We saw our political battles, even, as a privilege.""Few of us have been tested the way John once was," continued Obama, "Or required to show the kind of courage that he did. But all of us can aspire to the courage to put the greater good above our own. At John's best, he showed us what that means. And for that, we are all in his debt."Obama finished his written statement with condolences to the McCain family. "Michelle and I send our most heartfelt condolences to Cindy and their family."