That's an interesting question, but it doesn't really relate to Ron Paul.
He has not only called our entry into Iraq a mistake, he has called it "illegal" and "unconstitutional" - essentially accusing the President of crime, treason and malfeasance.
Had he kept his remarks calm and sane, your question might be more on point, but it isn't.
If a war is undertaken without a declartion of war, its unconstitutional and therefore illegal. You would agree that's not insane...that's just a fact.
I know that many people will claim that the Resolution was essentially a declaration of war that satisfies the Constitutional requirement...but, really that is a weak argument.
When you go back and read the debates of the Founders at the Constitutional Convention, they added that declaration requirement because they wanted to ensure that no President would ever the sole discretion to enter the US into a war. Giving the President the authority to enter into a war with Iraq "as he determines to be necessary and appropriate"...that's not a declaration of war...that is Congress essentially saying you don't need a declaration from us if you do decide to go to war. If Congress really meant to exercise its authority to declare war...why this Resolution 5 months before the actual invasion at a time when it was not known whether we would go to war?...why not a clear declaration when it was decided we needed to invade?
The only answer is political cowardice on the part of Congress
In 2002, Paul wrote:
Two weeks ago, during a hearing in the House International Relations committee, I attempted to force the committee to follow the Constitution and vote to declare war with Iraq. The language of Article I, section 8, is quite clear: only Congress has the authority to declare war. Yet Congress in general, and the committee in particular, have done everything possible to avoid making such a declaration. Why? Because members lack the political courage to call an invasion of Iraq what it really is- a war- and vote yes or no on the wisdom of such a war. Congress would rather give up its most important authorized power to the President and the UN than risk losing an election later if the war goes badly. There is always congressional "support" for a popular war, but the politicians want room to maneuver if the public later changes its mind. So members take half steps, supporting confusingly worded "authorizations" that they can back away from easily if necessary
Sounds to me like he's critical of Congress...not the President...specifically the political cowardice of people like Edwards, Hillary, Dodd, Biden, Kerry, et al. All of whom voted for the Resolution giving the President the power to invade Iraq...and now claim that they "wanted to give the inspections more time", "it was to make Saddam comply with inspections but they never thought the President would actually invade", yada yada. If you've seen any of the Democrats speak, you've heard all the excuses. That is exactly what Ron Paul predicted.