"But in practice, the so-called FISA court that issues such warrants functions as a virtual rubber stamp for the executive branch anyhow, so what's the great difference in the end?"

Which makes what Bush is doing all the more baffling. The court IS a virtual rubber stamp. So either he is full of himself (not to be discounted) or they were spying on people they knew even the court would not tolerate (e.g. John Kerry's campaign? Now before you call that too outrageous an accusation remember that Delay had the Department of Homeland Security track down the Democrats from the Texas State House who had fled the state in order to try to avoid the ethically challenged redistricting.)