No scoop here.  Woodward wrote the narrative on this back in his Plan of Attack in 2004.  Powell was saying to Bush over and over,  “You break it,  and you own it”

THE former American secretary of state Colin Powell has revealed that he spent 2½ hours vainly trying to persuade President George W Bush not to invade Iraq and believes today’s conflict cannot be resolved by US forces.

“I tried to avoid this war,” Powell said at the Aspen Ideas Festival in Colorado. “I took him through the consequences of going into an Arab country and becoming the occupiers.”

Of course,  this is also true, what Imitatio Christi: To: Colin Powell  says,  but I wonder if he read Woodward’s book. Powell did tell Woodward.  I myself am a little disappointed that Woodward didn’t raise more of a stink himself.  Frank Rich is not a big fan of Woodward because of this.

Powell tried to talk Bush out of war – Times Online