Here is my theory(s).
First, for Murtha, Kerry and who ever else voted for the authorization to go to Iraq, given the political environment of the time, it would have been viewed as political suicide to vote against it. Bush had snowballed the public into believing it was a noble fight. Given the spineless nature of politicians in the first place, I am not sure I could expect them to vote against it in that climate. Also, if they are elected to carry out the will of their constituents, would they not have had to vote for it regardless of their personal feelings. They are after all, supposed to represent we the people, right?
Which leads me to my next theory/question. Hypothothis: I, being a layman in a particular field hold belief "x". Along come several experts in said field who say that I am incorrect in my belief and they have the proof. Do I continue to hold my belief even in the face of 'proof' that my belief is not correct?
I do not know what level of access Senators or Congressman have in terms of intelligence access (I suspect not the same as POTIS/VPOTUS) so who do you trust? I would hope that the leaders of a country based on the rule of law would not lie about a issue as sensitive and important as going to war. Apparently we the people were wrong with that assumption.
I would like nothing better than to blame someone and say they 'should have known' something but I am not sure I can jump on that wagon. Part of being a good leader is surrounding your self we quality help. Another part is to ask the right questions. Bush Co. did neither. Most inside accounts from the Bush Co. indicates that he surrounds himself with people who will give him the answers he wants to hear. The end result is that the right questions are not asked or addressed such as; Is Rumsfled delusional when he says we will be welcomed like liberators? What do we do after "mission accomplished"? Will the american people support a drawn out conflict with thousands of our troops coming home in body bags? What are the political and religious dynamics in the region? Is there a governmental proposal which has broad support? Do the factions in Iraq get along? And the list goes on.
In my opinion, the POTUS did not want to know, the intelligence agencies did not make their opinions clear, no one gave answers to the questions that were not asked. Most importantly, no one wants to commit political suicide by voicing an unpopular opinion.
I believe you and I had a discussion a while back about a group (I forget who) who you and everyone else wanted censored. I gave the opinion that as long as no laws are violated, you cannot isolate one group even though their views are completely contrary to beliefs that most people hold. I despise the KKK but I will fight for their right to exist. My point being, I took a lot of grief (I think I finally got you to understand my position) but can you imagine a politician coming out with an unpopular view? Only since the war went down hill did the nay sayers come out of the wood work.
Yes, the politicians are cowards, but we elect them, we let them stay, and we hold them to standards that are out of whack. We expect them to vote against something we want, but would run them out of town on rail if they did.