I don't know what prescriptive power there is in it, but Ross Douthat's observation on the initial credibility of the Bush administration is, I think, a too often neglected insight on how America stumbled into Iraq:
If you had asked me, circa 1999, to pick out a group of senior GOPers who I would have wanted at the table in a national-security crisis - well, I'm not sure I could have done better than Colin Powell, Dick Cheney, Condi Rice and Donald Rumsfeld, with (in theory, though of course it didn't turn out that way) Brent Scowcroft whispering in Condi's ear, and George H.W. whispering in his son's. This is how the Bush Administration was sold to people, on foreign affairs at least, and I remember watching television after 9/11 and being so relieved to have Powell around, and Cheney, and Rummy, instead of, say, Anthony Lake or Madeleine Albright.
They were the "Vulcans," after all: Serious, steady, competent hands who, by sheer dint of experience and assumed seriousness, entirely eradicated concerns over a political neophyte's foreign policy acumen. Here's Charlie Rose interviewing Margaret Carlson:
ROSE: Where were you on the war?
CARLSON: I was, give diplomacy a chance. [Brightening] I was with Colin Powell the whole way along! Whatever Colin Powell—
ROSE: Oh, so whatever Colin— You know. OK.
CARLSON: Yeah. Whatever Colin does, I'll go with.
And as Yglesias occasionally points out, Tony Blair richly deserves a spot in the lineup too. This is a disillusionment Vietnam also triggered, but it's worth remembering that these guys -- save for Bush -- were not, in the initial analysis, recognized as a pantheon of fools and buffoons. It was war that exposed them as such, just as it did to McNamara and all the rest in Vietnam.
There's nothing wrong with using the positions of trusted figures in order to figure out your own leanings. A lot of policy research comes out in a given day and plenty of complicated conversations have already occurred -- it's impossible to navigate through it all without trusting the analyses of certain sources. But wars are a different matter. History shows they cannot be greenlighted on the assumption that fine leadership will elevate an unlikely undertaking. The leadership will fail, and so will the venture.