It pains me to write it, but there’s no avoiding the conclusion anymore that District Mayor Vincent Gray is either a fool or a liar — and I’m inclined toward the latter.

Tuesday’s guilty plea by former campaign official Thomas Gore, followed by Wednesday’s charges against another aide, shredded Gray’s credibility in the 14-month-old scandal.

It’s now getting close to impossible to believe the mayor’s past insistence that he was completely unaware of secret payments by his staff to oddball minor mayoral candidate Sulaimon Brown.

The alternate explanation is that Gray had no inkling of anything suspicious while Gore, a close associate of two decades, and campaign consultant Howard Brooks undertook a risky, illegal operation under his nose.

Gray is famous for his hands-on, detail-oriented management style. Which possibility seems more likely to you?

Washington, D.C. Mayor Vincent C. Gray sits behind a podium at a press conference at The Reef in Washington on May 23, the same day one of his former campaign officials pleaded guilty to bribing a rival candidate in 2010. (Ricky Carioti/THE WASHINGTON POST)

It’s disappointing for me to have become so mistrustful of the mayor. Like many others, I was sympathetic when he mounted a late challenge to Adrian Fenty and won the Democratic primary by nearly 10 percentage points.

I had been impressed with Gray’s leadership as chairman of the D.C. Council. He was not a career politician but had run for D.C. Council for the first time in 2004 at age 61 after years of work in the nonprofit community helping mentally retarded people and homeless youth. He projected authority and gravitas, and people in and out of city government said he was honest.

“People had hope in electing a Vincent Gray who was a Washingtonian who they thought was a good chairman, had a businesslike approach and none of this cronyism” associated with Fenty, said Dorothy Brizill, a veteran community activist and executive director of the good-government organization DCWatch.

“Now they are scratching their heads and saying, ‘Did he fool us?’ We thought we knew this man,” she said.

In retrospect, it seems that the Gray campaign seized on illicit shortcuts to help defeat Fenty, partly because it was so concerned that the incumbent was starting off with such a big advantage in finances.

The sleazy measures included the covert payments to Sulaimon Brown, ostensibly a rival in the mayor’s race. Gray’s team wanted Brown to continue shrill, over-the-top verbal assaults that weakened Fenty in campaign debates.

“I think he [Gray] is basically honest. But in the craziness of campaigns, things happen, and afterward, you go, ‘What was I thinking? With 20-20 hindsight, I never would have let that happen,’ ” said a longtime District politician, who spoke on the condition of anonymity to avoid offending the mayor.

As I’ve written before, U.S. Attorney Ronald C. Machen Jr.’s aggressive investigation into the campaign threatens to make Gray’s administration a “lost term.” It’s hard to fulfill promises to create jobs and improve schools when you’re preoccupied with staying out of jail.

Although Gray hasn’t been implicated in court documents, we now know that both Gore and Brooks are cooperating with Machen’s team, whose ultimate target is almost certainly the mayor. Machen is looking not only at the payments to Brown — which were fairly small sums — but also at signs of a much bigger “shadow campaign” fueled by questionable campaign contributions.

With active involvement from at least two key people, a lot of seamy stuff might come to light.

The guilty plea by Gore was especially important because he’s been so close to Gray, having served as his principal finance official for three campaigns. Previously, it was possible to think that even if Brown was mostly telling the truth, maybe the payments were orchestrated just by Brooks, who was more removed from Gray.

Gray also looks bad because, on the advice of his attorney, he’s turned mum about the case. He’s stopped making those passionate public statements that he, personally, knew nothing about any payments and found it “incredible” that any of his aides would have made them.

Such silence is going to become wearing as the investigation continues. “The mayor should say what he knows and when he knew it,” said council member Muriel Bowser (D-Ward 4), who chairs the Committee on Government Operations.

That, of course, paraphrases the famous question posed about Richard Nixon in the Watergate scandal. And we know how that turned out.

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