Arizona Senator John McCain, a long-time leader of the Republican Party and a bona fide old lion of the U.S. Senate, has been diagnosed with an aggressive and malignant form of brain cancer. Surgeons removed the tumor this week, but the Vietnam war hero and former Presidential candidate knows he is facing the fight of his life. This kind of tumor tends to come back, so McCain’s treatment has to be as aggressive as the cancer.

The unavoidable truth is that Senator McCain has an ethical obligation to resign, and the sooner the better. Members of Congress, like Supreme Court Justices, should not drag their tenure into advanced age, when health, energy and mental acuity are likely to decline. McCain, who is 80, has shown unusual vigor as he has aged, but it is absurd to  imagine that he can do his job while undergoing life-and-death cancer treatments. For his own sake, that of his party, the institution of the Senate, his nation and his legacy, Senator McCain needs to be an exemplar to his colleagues and future elected officials who have the public’s trust. It is a time for him to model sacrifice, selflessness, humility and good judgment.

There is important work to be done, and if it is to be done well, men and women of health and focus must be the ones to do it. John McCain is an amazing and honorable man who doesn’t have to prove his mettle and fortitude to anyone. Now he has to have the courage and integrity to do the hardest thing of all: to know when to quit, and to do it.

I’m betting that he will. John McCain knows how to be a hero.