Can a presidential candidate justify a long and friendly relationship with someone who, back in the 1970s, extolled violence and committed crimes in the name of a radical ideology -- and who has never shown remorse or admitted error? When the candidate in question is Barack Obama, John McCain says no. But when the candidate in question is John McCain, he's not so sure.

Obama has been justly criticized for his ties to former Weather Underground member Bill Ayers, who in 1995 hosted a campaign event for Obama and in 2001 gave him a $200 contribution. The two have also served together on the board of a foundation. When their connection became known, McCain minced no words: "I think not only a repudiation but an apology for ever having anything to do with an unrepentant terrorist is due the American people."

What McCain didn't mention is that he has his own Bill Ayers -- in the form of G. Gordon Liddy. Now a conservative radio talk show host, Liddy spent more than four years in prison for his role in the 1972 Watergate burglary. That was just one element of what Liddy did, and proposed to do, in a secret White House effort to subvert the Constitution. Far from repudiating him, McCain has embraced him.

How close are McCain and Liddy? At least as close as Obama and Ayers appear to be. In 1998, Liddy's home was the site of a McCain fundraiser. Over the years, he has made at least four contributions totaling $5,000 to the senator's campaigns -- including $1,000 this year.

Last November, McCain went on his radio show. Liddy greeted him as "an old friend," and McCain sounded like one. "I'm proud of you, I'm proud of your family," he gushed. "It's always a pleasure for me to come on your program, Gordon, and congratulations on your continued success and adherence to the principles and philosophies that keep our nation great."

Which principles would those be? The ones that told Liddy it was fine to break in to the office of the Democratic National Committee to plant bugs and photograph documents? The ones that made him propose to kidnap antiwar activists so they couldn't disrupt the 1972 Republican convention? The ones that inspired him to plan the murder (never carried out) of an unfriendly newspaper columnist?

Liddy was in the thick of the biggest political scandal in American history -- and one of the greatest threats to the rule of law. He has said he has no regrets about what he did, insisting that he went to jail as "a prisoner of war."

All this may sound like ancient history. But it's from the same era as the bombings Ayers helped carry out as a member of the Weather Underground. And Liddy's penchant for extreme solutions has not abated.

In 1994, after the disastrous federal raid on the Branch Davidian compound in Waco, he gave some advice to his listeners: "Now if the Bureau of Alcohol, Tobacco and Firearms comes to disarm you and they are bearing arms, resist them with arms. Go for a head shot; they're going to be wearing bulletproof vests. … Kill the sons of bitches."

He later backed off, saying he meant merely that people should defend themselves if federal agents came with guns blazing. But his amended guidance was not exactly conciliatory: Liddy also said he should have recommended shots to the groin instead of the head. If that wasn't enough to inflame any nut cases, he mentioned labeling targets "Bill" and "Hillary" when he practiced shooting.

Given Liddy's record, it's hard to see why McCain would touch him with a 10-foot pole. On the contrary, he should be returning his donations and shunning his show. Yet the senator shows no qualms about associating with Liddy -- or celebrating his service to their common cause.

How does McCain explain his howling hypocrisy on the subject? He doesn't. I made repeated inquiries to his campaign aides, which they refused to acknowledge, much less answer. On this topic, the pilot of the Straight Talk Express would rather stay parked in the garage.

That's an odd policy for someone who is so forthright about his rival's responsibility. McCain thinks Obama should apologize for associating with a criminal extremist. To which Obama might reply: After you.