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 would n'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 could n'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 do n'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 did n'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 do n't ! '' Oh yes you do . Perry spent days trying to recover from a brain freeze in which he could n'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 was n't as bad as Cain 's Libya moment . `` The only thing Perry could n'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 could n'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 ca n't possibly happen again . The opinions expressed in this commentary are solely those of Gloria Borger .
Gloria Borger : Herman Cain seems to know little about national issues , presidency . She says he has n't adequately dealt with allegations of sexual harassment . Cain seemed to have little sense of U.S. policy on Libya , Borger says . Borger : The former CEO of Godfather's Pizza is running for president as a Republican and the first Mormon in American history.