On Friday night, Herman Cain was a fly and David Letterman was the spider cordially inviting Cain to "step into my parlor." Didn't Cain or any of his advisors see the potential for disaster in Cain appearing on Letterman's show? 

Didn't anybody say, "Herman, don't go in there! It's a trap!"?

I desperately don't want to be seen as one of those just itching for clear proof that Herman Cain's candidacy is over. But it's hard to have watched Cain on Letterman and not come to the conclusion that neither Cain nor his advisors have sufficiently good judgment for him to be president.

I've been aware of Cain, and impressed by him, ever since I first heard him on the radio in Atlanta. I was ecstatic when he announced he was seeking the Republican nomination.

I have long maintained, long before anybody ever heard of Barack Obama, that a backlash of conservative Blacks might be the only thing that could save this country. The election of Barack Obama seemed to make that less likely, but I "kept hope alive".

And Herman Cain re-kindled that hope. I saw him as the man who could lead Black Americans off the Democrat plantation and, when that happened, many liberal whites would follow.

I was not deterred by the allegations of sexual harassment, nor by the "pause that depresses" when he was asked about Libya. I was not deterred by Cain's apparent lack of comprehensive foreign policy knowledge; I figured he would surround himself with competent advisors and that his own instincts and managerial and leadership skills, and his belief in America and its -- and his own -- general goodness would see him through.

But Cain's appearance on Letterman's show has seriously undermined my confidence in Cain's judgment and in his ability to choose competent advisors. Anybody who's watched Letterman over the past decade should know that the only agenda that gets advanced on Letterman's show is his own. Cain's appearance was a losing proposition going in.

Granted, Cain is a nice man, and appeared as such. He probably thought that would count for something. It did not. Letterman took the interview in the direction he wanted to take it, while maintaining his own veneer of "niceness" and cordiality.

It was clear to me that Letterman had his interview strategy and tactics well-planned and mapped-out. Cain had his "talking points", but it seemed that, in contrast to Letterman, Cain was "winging it."

The times that Cain probably thought he was being forceful, he still wasn't nearly forceful enough. He never really challenged Letterman's control of the interaction.

When Letterman exploited the issue of Cain's campaign manager, Mark Block, smoking a cigarette on an internet campaign commercial (Letterman even cut to a shot of Block taking deep drags and grinning), I wanted Cain to say, "Wait a minute! It's OK for Barack Obama to smoke, but not for one of my advisors?" Instead, as he did over and over throughout the interview, Cain allowed Letterman to put him on the defensive.

And it also didn't help that Cain's response to one of Letterman's questions struck me as one of the most vapid things he could possibly have said. When Letterman asked, "What's the difference between you and Donald Trump?", Cain responded, "He's white and I'm black." That, for me, was probably the most cringeworthy moment of the entire interview.

In his promos for the Cain interview, Letterman said, "The road to the White House goes through me!" Maybe so, but only in the sense that Letterman has enormous power to block that road for any candidate he opposes, and that power only increases when the candidate, in a colossal lapse of good judgment, steps blithely into Letterman's parlor.