Editor's note: Gloria Borger is CNN's chief political analyst, appearing regularly on shows such as "AC360," "The Situation Room," "John King USA" and "State of the Union." Republican presidential candidates take on national defense, the economy, international relations and terrorism issues in the CNN Republican National Security Debate in Washington, D.C.., moderated by Wolf Blitzer at 8 p.m. ET Tuesday, November 22, on CNN, the CNN mobile apps and CNN.com/Live.
Washington (CNN) -- It's hard to remember a presidential candidate who seemed more, er, unacquainted with the national dialogue -- or presidential prerequisites -- than Herman Cain.
At first, he seemed a likable enough fellow. With exactly one idea: a 9-9-9 tax system. Not a truly GOP-minted plan, since it includes a national sales tax, which Republicans loathe. But never mind. He was genial and a welcome addition to those early debates in which some of his fellow contenders seemed so humorless, angry and, in some cases, downright unfriendly.
Of course, Cain was unfriendly in that first moment in which he said he wouldn't allow any Muslims to serve at high levels of government (now a Cain classic!). But he backtracked, so the matter seemed to slip away.
That's because Cain was still a gadfly -- one of those folks never destined to get the center podiums at the debates. Not serious, and not a serious threat.
But as the weeks wore on, Cain became a phenom. Maybe it was the anti-Mitt Romney element. Or the likability factor. Or the anti-politician crowd gone wild.
Eventually, he rose to the top of the pack. (Think helium.)
But when the gaffes continued -- and the sexual harassment allegations surfaced -- it was no longer harmless. Cain became a parody of the empty-suit candidate, and his campaign proudly carried his baggage. A silly Web ad with the campaign manager taking a drag of a cigarette said it all: grabbing for attention, blowing nothing but smoke.
As for the sexual harassment allegations, the man-who-would-be-president alternately couldn't recall them or could mildly recall them. The National Restaurant Association, where Cain worked at the time, recalled one settlement just fine. But Cain never asked for the records to be released to clear his name, so his name remains far from cleared.
And don't expect the woman he recently dubbed "Tutti-frutti" -- U.S. Rep. Michele Bachmann -- to bail him out either.
If this is the way Cain wants to behave, I suppose it's a free country. But there is a cost to Republicans.
The pursuit of the presidency is a serious undertaking. It requires ideas, beliefs, preparation, discipline, diligence. It is not vaudeville (although it may sometimes look that way). And it's not a book tour or the ticket to a future TV deal (although it may sometimes look that way.) To state the obvious, the president is the person who sends our sons and daughters to war, who manages the economy, who is our face to the world.
So when I speak with Republicans who have been around awhile and who have served in top government jobs, Cabinet posts or even in the White House, they're genuinely upset. Not because they support Romney or Rick Perry or Newt Gingrich, but because they believe that Cain just might be sucking all of the oxygen out of the GOP race. And, more to the point, they worry his antics -- and his behavior -- could bleed onto the GOP field, as if the pursuit of beating Barack Obama is somehow trivial. While the other candidates treat him like the silly uncle, he's becoming dangerous to their own brand.
Sure, there are always inadequate presidential candidates. But here's where Cain truly distinguishes himself: he defends his inadequacies, even wears them as a badge of honor. So what if he didn't know the president's Libya policy? "I'm not supposed to know anything about foreign policy period. Just thought I'd throw that out," he told the Milwaukee Journal-Sentinel this week -- the same day as the Libya gaffe. 'I want to talk to commanders on the ground. Because you run for president (people say) you need to have the answer. No, you don't!"
Oh yes you do.
Perry spent days trying to recover from a brain freeze in which he couldn't remember the name of a government agency he wanted to eliminate, because he knew he made a real mistake. It was bad, but it wasn't as bad as Cain's Libya moment. "The only thing Perry couldn't remember was the name of a Cabinet agency," Todd Harris, GOP political consultant who is unaffiliated with any of the campaigns, told CNN's Kevin Bohn. "For Cain, it looked like he couldn't remember what he actually believes."
So far, no other candidates are defending Cain's behavior and lack of serious intent or world view. No one is saying it's a good thing not to know what side we are on in Libya. But they're not hitting him for it either, as they should. And who is going to be the first serious GOP candidate to come out and say more about the harassment charges other than calling them "troubling?"
I'll give you this: It was far worse with Sarah Palin. After she was chosen as John McCain's running mate, everyone whispered she was inadequate -- but said nothing publicly. In trying to win, the party became complicit in defending an indefensible choice.
That can't possibly happen again.
The opinions expressed in this commentary are solely those of Gloria Borger.