I think its serious and he is exercising good judgement.
This is serious, this is a country-first move on Sen. McCain's part (he IS a sitting Senator after all) and besides, this move is in keeping with his maverick reputation...he apparently does what he believes is right, regardless of whether the pundits or congress critters agree.
Good for John. I am respecting you more and more (even tho I hate for you to miss a chance to clean bammies clock in a debate! )
Besides, what can a 2-yr junior senator offer of substance? Particularly one who has spent most of that time campaigning....and now, apparently doesn’t know how to do anything else.