He, like President Lyndon Johnson and other Americans in high positions,  shielded the state of Israel from legal recourse following the IDF's (Israeli Defense Forces) June 8, 1967, attack on the USS Liberty, in which 34 U.S. servicemen were murdered and another 172 were seriously wounded.
The attack was a criminal act of war; the ensuing cover-up constituted acts of treason; and Admiral McCain was one of many high U.S. officials who, for political reasons, hastily sided with the foreign aggressor over the U.S. servicemen who endured the act of aggression.
Thirty years after the massacre, on March 8, 1997, American peace activist, William Hughes, sent a letter to the admiral's son, Senator John McCain, requesting that he do his dutiful part in demanding that Congress investigate, once and for all, the attack on the USS Liberty— this time, allowing full disclosure of evidence including eyewitness accounts of 60 USS Liberty staffers whose written testimonies were kept out of the original sham of an investigation.
The response Hughes received was unsettling, to say the least:
McCain declined my offer to raise his voice on behalf of the Liberty. He said that he wasn't going to do anything about it because the "matter was thoroughly reviewed." Really! In his letter to me, dated, April 28, 1997, he relied on the results of the now totally discredited Naval Court of Inquiry, which was conducted by Rear Admiral Isaac Kidd, USN. It began on June 10, 1967, and lasted less than a week. A scathing and devastating rebuttal of that seriously flawed Naval Inquiry can be found in the "Declaration," dated Jan. 8, 2004, of Capt. Ward Boston, Jr., JAGC, USN (Ret). . . .So, McCain, the "Conscience of the Senate" wasn't going to do anything about bringing justice to the Liberty! He did, however, say something else in his letter that made me feel suspicious about his do-nothing position. He said, "The attacking nation" did not submit any evidence or testimony on their behalf about the assault at the inquiry. "Attacking nation!" What is that suppose to mean? Why couldn't McCain just come right out, he is the "Conscience of the Senate" after all, and simply say: The Israelis? Why use a deceptive term, like: "attacking nation?" Talk about Orwellian Double Speak! I can't imagine McCain writing about the attack on U.S. forces at Pearl Harbor, on Dec. 7, 1941, and instead of stating up front that Japan was responsible, refer to that sneaky, militant aggressor as the "attacking nation." - Advertisement -
But to say that exchange, alone, qualifies as treason would be half-baked. After all, most Members of Congress are in the back pocket of the indomitable Israel lobby—some more disgracefully than others. But not all of them are running for president, and not all of them are on record as taking part in the utter pillaging of the U.S. Constitution and the Bill of Rights to the extent McCain and so many other lawmakers have. Most of them, maybe, but not all.
The following is a cursory rundown of major Congressional measures voted for, or co-sponsored, by John McCain; all of which have subverted the rule of law by stripping U.S. citizens of their inalienable rights under the Declaration of Independence and the Constitution. Many of which were lobbied for, primarily, by members of the Israel lobby—namely, AIPAC.
The PATRIOT Act, winner of the Orwellian Name of the Millennium award, is summed up well by the only Republican candidate for president worth voting for—Congressman Ron Paul:
The PATRIOT Act severely eroded the system of checks and balances by giving the government the power to spy on law abiding citizens without judicial supervision. The several provisions that undermine the liberties of all Americans include: sneak and peak searches; a broadened and more vague definition of domestic terrorism; allowing the FBI access to libraries and bookstore records without search warrants or probable cause; easier FBI initiation of wiretaps and searches, as well as roving wiretaps; easier access to information on American citizens' use of the internet; and easier access to e-mail and financial records of all American citizens. 
The Military Commissions Act, according to Dr. No:
"grants excessive authority to use secretive military commissions outside of places where active hostilities are going on. The Military Commissions Act permits torture, arbitrary detention of American citizens as unlawful enemy combatants at the full discretion of the president and without the right of Habeas Corpus, and warrantless searches by the NSA (National Security Agency). It also gives to the president the power to imprison individuals based on secret testimony." - Advertisement -
The Bipartisan Campaign Reform Act violates the First Amendment:
Also known as the McCain-Feingold act, this little gem regulates political speech by erecting limits to who can donate what, how soon before an election, as well as who can talk about a politician, or make "political" statements. The alleged intent of the act is to prevent influence buying on the part of corporations, wealthy individuals or foreign governments by limiting campaign donations, and "electioneering speech." As usual, the act completely misses the real problem, addressing only the symptoms. One probable intention of the act is to tip the balance of power in favor of incumbents and the Republicrat party by limiting political speech. 
The Gun Show Loophole Closing and Gun Law Enforcement Act of 2001 chips away at the Second Amendment where the Brady Bill left off:
Senator McCain, our Republican from Arizona, an open carry state with average crime rates wants to expand the Brady Bill to close a "loophole" that allows private citizens to buy and sell guns to each other at gun shows, fund new gun control programs, and expand the BATF. Wouldn't a true conservative support the repeal of the awful Brady Law? No. He's expanding it, which is especially weird since he voted against it eight years earlier.