All of lies, justifications, and rationales for invading and occuppying Iraq center around the notion that it would somehow make America safer. WMD, toppling Saddam, spreading democracy, securing our oil supply ... everyone who supported the invasion did so because they believed it would make us safer.
If the invasion and occupation of Iraq has not made us safer, then every American soldier who died there died in vain.
The true intentions of those who lied us into the war may not matter -- whether it was to secure our oil, punish those who scare them, or impose democracy at the barrel of a gun. What matters most is that every one of their justifications rested on making America safer. If America is not safer, then every American who died in Iraq died in vain. (Note that I am not including Afghanistan).
If American troops died in vain, then those responsible must be held to account by convincing voters that American troops died in vain in a war based on lies. Polls should ask not if the "war" was worth it, but "have our troops died in vain if America is not safer?" That properly frames the debate.
Republicans equate Democrats with being traitors who side with our enemies. Democrats must equate Republicans with being murderers for making our brave soldiers die in vain for an occupation that has made America weaker, more vulnerable, and less safe. America has suffered over 20,000 casualties for nothing. Their deaths and wounds have not advanced the war on terror, secured our oil, promoted democracy, weakened Osama, or made us safer.