Why would the normally stoic senator become so hyperbolic about a ruling that, at its essence, strengthens the vitality of the "Great Writ" of habeas corpus - a bedrock constitutional right?
There are several reasons. As a political matter, McCain clearly understands that in his quest to enchant the hard-right wing of the Grand Old Party, he must rail upon the Supreme Court whenever it happens to disagree with the Bush Administration on legal aspects of the war on terrorism.
This is why, just a few weeks ago, McCain delivered a speech that hammered the federal judiciary, any lingering notion that he intends to govern as a moderate on legal policy and priorities.
So, whether or not McCain really believes what he says, it is good politics (read: inaccurate and unfair) to declare that the Court just sided with the terrorists over the President when five Justices ruled that the terror suspects detained in Cuba may challenge their detentions in our civilian courts.
And it is good politics to warn of the detainees clogging those courts with frivolous lawsuits - like current domestic prisoners do - even though the suspects so far only have sought to have some sort of objective, neutral fact-finder evaluate the government's classification of them as "enemy combatants."
The main reason for McCain's strong language, however, is as personal as political.
Following the last Supreme Court ruling on this topic, which also struck down stubborn Administration detainee policies, the Senator (a Vietnam torture victim himself) invested no small amount of his own treasured (and well-earned) historical capital to try to broker a deal on the detainees.
And, in late 2006, he did.
It's called the Military Commissions Act. It was a terrible idea from the very beginning, and it was one of two federal statutes undercut by the Justices last Thursday. It's no wonder the nominee is taking the defeat personally.
After first insisting that federal law clearly and unambiguously outlaw "torture," McCain suddenly caved to White House pressure on the MCA, allowing the Administration to insert into the law a clause that effectively allows (and, indeed, legally buttresses the efforts of) the executive branch to implement torture as a means of interrogation.
Without McCain's pander, there would have been no bad law for the Court to strike down last week. Without McCain's grandiloquent appeal to Democrats and moderates during that lame-duck session, there quite possibly might have been a better law that just might have passed its constitutional test this term.
McCain's sell-out on the torture language is not the reason the Justices declared the MCA unconstitutional. It is not the reason why the detainees now have more access to federal courts than they did before. But it is emblematic of the larger and much more destructive, seven-year-long sell-out of the legislative branch in the legal fight against terrorism.
And that emblem, thanks to the Supreme Court, now has John McCain's face on it just in time for the run-up to the general election.
This is not necessarily fair. It's not just John McCain who failed or refused to do the right thing. Last week's ruling was the fourth defeat in a row for the Administration at the Supreme Court. And on the past three occasions the Congress has responded not by embracing the hints and clues left by the Court's majorities - by, say, brokering a desperately-needed deal between executive and judicial branches over a terror law policy - but by siding with the White House.
McCain and other so-called "moderates" have had the power for years to avoid these Supreme Court showdowns and show-ups. They just haven't had the political courage to exercise that power.
All of which means the Supreme Court isn't the only reason why the terror detainees remain in legal limbo. The White House is to blame for pushing beyond the legal limits of executive power. And the Congress is to blame for allowing it to happen despite entreaties by the judiciary for help.
If I were a good man like McCain, I'd be embarrassed by this. And perhaps he is. And perhaps that embarrassment is expressing itself in anger instead of consideration. In any case, it's misguided.
Contrary to the angry candidate's remarks, last week's Boumediene ruling is not on a par with the Court's 1857 Dred Scott decision that tagged slaves as "property;" its 1896 Plessy v. Ferguson decision that endorsed the "separate but equal" doctrine; or its Korematsu v. United States decision that affirmed the detention of Japanese-Americans during World War II.
In fact, the recent ruling on detainee rights will be revered, not reviled, by future generations, who will study the first decade following the terror attacks on America with a curious mix of regret and sadness about lost opportunities, legal and otherwise, that hampered our collective response.