When considering John McCain's history of unethical behavior, the list usually starts (and ends) with the Keating Five scandal in the 1980s, for which McCain was rebuked by the Senate Ethics Committee. In the aftermath, McCain helped improve his public image, and bury the scandal, by becoming an advocate of campaign-finance reform.

But the notion that McCain cleaned up his act may not be entirely true. Take, for example, Donald Diamond, a wealthy Arizona real estate developer and generous McCain contributor, who wanted some coastal land in California freed up by an Army base closing.

When Mr. Diamond wanted to buy land at the base, Fort Ord, Mr. McCain assigned an aide who set up a meeting at the Pentagon and later stepped in again to help speed up the sale, according to people involved and a deposition Mr. Diamond gave for a related lawsuit. When he appealed to a nearby city for the right to develop other property at the former base, Mr. Diamond submitted Mr. McCain's endorsement as "a close personal friend."

Writing to officials in the city, Seaside, Calif., the senator said, "You will find him as honorable and committed as I have."

Courting local officials and potential partners, Mr. Diamond's team promised that he could "help get through some of the red tape in dealing with the Department of the Army" because Mr. Diamond "has been very active with Senator McCain," a partner said in a deposition.

For Mr. McCain, the Arizona Republican who has staked two presidential campaigns on pledges to avoid even the appearance of dispensing an official favor for a donor, Mr. Diamond is the kind of friend who can pose a test.

The closer one looks at this, the worse it appears. A McCain aide described the senator's efforts as "a constituent matter," but there's ample reason to believe it was much more than that.

McCain helped a wealthy and generous donor buy land from the Army -- complete with special water rights -- for a quarter of a million dollars, which McCain's buddy then sold two years later for $20 million. There's a term for this -- it's called "influence peddling," and it's exactly the kind of thing McCain swears he never gets involved with.

If the Tony Rezko story was considered a big deal by campaign reporters, the Donald Diamond issue should be huge.