Suppose the president undertook surveillance for foreign intelligence, in violation of FISA. That is, without a warrant, and on purely domestic communications. Or a real life case from 1994, tossing somebody's house without a warrant, in violation of FISA.
Suppose further that the case is litigated as a violation of FISA. Do you think the law would be upheld, or would the "illegal" activity be allowed, found to be an impermissible legislative restriction on the power of the executive?
I do agree with your read of FISA, by the way. I disagree that the warrantless part is limited to NSA. NSA is collecting purely domestic traffic without a warrant, all of the time. In a typical marvel of legal fiction, the law view this as "not surveillance."
In your example, the President would be in violation of USC 50. FISA would still be legal (at least, according to 2 lower court rulings) as the President did not submit a request for FISA warrants. The exception would be that active intelligence lead the Executive branch to believe a credible threat of terrorist attack was imminent. Or, if a non-US citizen was considered a "lone wolf" and in preparation for a terrorist act on domestic soil.
I do agree with your read of FISA, by the way. I disagree that the warrantless part is limited to NSA.
My apologies if I implied that. I was merely suggesting that NSA also does warrantless surveillance.