In the above a specific potential threat is outlined, the "IF" and "COULD" clearly define it as a potential threat. GWB then went on to say:

"Facing clear evidence of peril, we cannot wait for the final proof -- the smoking gun -- that could come in the form of a mushroom cloud."

That is a general statement of principle of how a responsible government should react.

"IF" and "COULD" are most definitely not considered grounds for attacking another country. It is especially not the behavior of a responsible government to use "IF" and "COULD" as its reasons for attacking another country.