(CNN) It will take more than a devastating diagnosis to keep John McCain out of the heat of political battle.

The Arizona senator makes a poignant return to the Senate on Tuesday, less than a week after learning he has an aggressive form of brain cancer, just in time to boost tricky GOP vote math on the wobbling bid to replace Obamacare.

McCain's return comes as he considers treatment options for the latest fight of a lifetime of military heroism and political combat that has made him one of America's most enduring public figures.

There will likely be emotional scenes when the grizzled Senate warrior arrives amid his colleagues in the chamber, following a rare bipartisan outpouring of shock and sympathy for the 80-year-old former presidential nominee.

His quick return, after securing the permission of his doctors to make the long cross-continental flight, fits the character of a senator who still keeps a frenetic schedule that would humble a younger man, and has shown he has no interest in retirement.

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