Actually what they say in the article is not entirely correct. There is third way and this was proven in 2006 when the judges reviewed claims that Bush bypassed the courts: From the WT 2006 article:
A panel of former Foreign Intelligence Surveillance Court judges yesterday told members of the Senate Judiciary Committee that President Bush did not act illegally when he created by executive order a wiretapping program conducted by the National Security Agency (NSA).
The five judges testifying before the committee said they could not speak specifically to the NSA listening program without being briefed on it, but that a Foreign Intelligence Surveillance Act does not override the president’s constitutional authority to spy on suspected international agents under executive order.
“If a court refuses a FISA application and there is not sufficient time for the president to go to the court of review, the president can under executive order act unilaterally, which he is doing now,” said Judge Allan Kornblum, magistrate judge of the U.S. District Court for the Northern District of Florida and an author of the 1978 FISA Act. “I think that the president would be remiss exercising his constitutional authority by giving all of that power over to a statute.”
There is possibly a fourth way - allies could do the spying for us, as Larry Johnson says.