Bush's deliberate deception is perpetrated by the rhetorical trick of juxtaposing two statements. In essence he says, over and over: "We must invade Iraq to advance the war on terror. We are engaged in the war on terror because of September 11th". If A = B and B = C, then A = C.

You can verify this yourself by going to whitehouse.gov and reading any of Bush's statements on the subject(s). Here are the relevant excerpts from Bush's September 7th speech, with the "filler" removed to reveal the pattern of juxtaposition:

THE PRESIDENT: Good evening. I have asked for this time to keep you informed of America's actions in the war on terror.

... deadly attacks on our country ... systematic campaign against terrorism. ... And we acted in Iraq ... September the 11th, 2001 ... September the 11th ... Iraq ... Iraq ... Iraq ... Iraq ... Iraq ... terrorists ... Iraq ... Iraq ... Saddam Hussein ... terrorists ... Saddam ... Islam ... terrorists ... Iraq ... terrorists ... war on terror ... Iraq is now the central front ... in the war on terror ... Iraq ... Iraq ... terrorists ... Iraq ... Iraqis ... terrorists ... the Iraqi people ... Iraqi citizens ... terrorists ... Iraq ... Iraq ... Iraq... Saddam Hussein ... Terrorists in Iraq ... Iraq ... the Iraqi people ... Iraq ... Iraq ... Iraq ... Iraqi police ... Iraqi border guards ... Iraqi army ... Iraqi citizens ...Iraq ... Iraq ... the Iraqi people ... Iraq ... Iraq ... Iraq ... Iraq ... Iraq ... Iraq ... terrible weapons ... September the 11th, 2001 ... terrorist attacks ... fighting that enemy in Iraq ... war on terror ... the great cause ... the 'front lines of freedom.' ... war on terror

Transcript at whitehouse.gov

The fact that you've so far had trouble perceiving the pattern is testimony that it's working; that and the fact that over 70% of your fellow citizens have fallen for it too. Can you see now how the trick is performed?

Gary Larson captured the essence of the trick years ago in a Far Side cartoon. This is how Bush's speechwriters see us: