His purpose is irrelevant to the act itself. If the constitution/fisa law says get a warrant, even retroactively, then he better get a warrant. The burden is on the president to show a valid reason why he committed a felony.
Why do you think he ordered the phone taps prior to the Al Qaeda threat?
I don't think it's irrelevant at all. You compared him to Nixon. Not sure if you were around when we first discussed warrantless wiretaps, but I've never approved of them. I do, however, draw a distinction between acts done for (at least the perceived) benefit of the country, versus a criminal like Nixon.
I'm not sure if and/or why he ordered warrantless taps before 911, but didn't Clinton do the same thing? Regardless, I'm pretty certain he was provided some kind of legal counsel.
But you didn't answer my question about the purpose. I understand the argument people make about oil. What I'm trying to understand is the rational for concluding Bush intentionally broke the law by spying. What did he have to gain?