The US Constitution Article II, Section 3

[BWahlberg]

Section 4 - Disqualification

The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.

-<Scope and Limits of FISA>-

For most purposes, including electronic surveillance and physical searches, "foreign powers" means a foreign government, any faction(s) or foreign governments not substantially composed of US persons, and any entity directed or controlled by a foreign government. §§1801(a)(1)-(3) The definition also includes groups engaged in international terrorism and foreign political organizations. §§1801(a)(4) and (5). However, the sections of FISA authorizing electronic surveillance and physical searches specifically exclude their application to groups engaged in international terrorism. See §1802(a)(1) (referring specifically to §1801(a)(1), (2) and (3)).

The statute limits its application to US persons. A US person includes citizens, lawfully admitted permanent resident aliens, and corporations incorporated in the US.

The code defines "foreign intelligence information" to mean information necessary to protect the United States against actual or potential grave attack, sabotage or international terrorism.[3]

-<News story from the NY times>-

On December 16, 2005, The New York Times printed a story that, under White House pressure and on the authority of an executive order from President George W. Bush, the National Security Agency had been conducting warrantless phone-taps on people in the U.S. calling people outside of the country, in an attempt to combat terrorism. [3]

Under a presidential order signed in 2002, the intelligence agency has monitored the international telephone calls and international e-mail messages of hundreds, perhaps thousands, of people inside the United States without warrants over the past three years in an effort to track possible "dirty numbers" linked to Al Qaeda, the officials said. The agency, they said, still seeks warrants to monitor entirely domestic communications.
According to the Times:

The White House asked The New York Times not to publish this article, arguing that it could jeopardize continuing investigations and alert would-be terrorists that they might be under scrutiny. After meeting with senior administration officials to hear their concerns, the newspaper delayed publication for a year to conduct additional reporting. Some information that administration officials argued could be useful to terrorists has been omitted.