Conservatives have tried to justify his actions by saying that Clinton and Carter did the same thing. Only, they didn't. They made up the part about Clinton and Carter doing the same thing. As explained by georgia 10 at Daily Kos, the orders they signed were expressly authorized by a statute specifically addressing the issue, didn't involve American citizens, and Clinton's order didn't even involve wiretaps:
CLINTON DID NOT ORDER WARRANTLESS SEARCHES OF AMERICAN CITIZENS
Here's what Clinton signed:
Section 1. Pursuant to section 302(a)(1) [50 U.S.C. 1822(a)] of the [Foreign Intelligence Surveillance] Act, the Attorney General is authorized to approve physical searches, without a court order, to acquire foreign intelligence information for periods of up to one year, if the Attorney General makes the certifications required by that section.
You don't have to be a lawyer to understand that Clinton allowed warrantless searches if and only if the AG followed section 302(a)(1). What does section 1822(a) require?
* the "physical search is solely directed at premises, information, material, or property used exclusively by, or under the open and exclusive control of, a foreign power or powers." Translation: You can't search American citizens.
* and there is "no substantial likelihood that the physical search will involve the premises, information, material, or property of a United States person." Translation: You can't search American citizens.
Moreover, Clinton's warrant waiver consistent with FISA refers only to physical searches. "Physical searches," as defined by 1821(5), exclude electronic surveillance.
CARTER DID NOT AUTHORIZE WARRANTLESS SEARCHES OF AMERICAN CITIZENS
And now, Carter's turn:
1-101. Pursuant to Section 102(a)(1) of the Foreign Intelligence Surveillance Act of 1978 (50 U.S.C. 1802(a)), the Attorney General is authorized to approve electronic surveillance to acquire foreign intelligence information without a court order, but only if the Attorney General makes the certifications required by that Section.
Here, Carter refers to "electronic surveillance," rather than "physical searches" like Clinton. But again, Carter limits the warrantless surveillance to the requirements of Section 1802(a). That section requires:
* the electronic surveillance is solely directed at communications exclusively between or among foreign powers. Translation: You can't spy on American citizens.
* there is no substantial likelihood that the surveillance will acquire the contents of any communication to which a United States person is a party. Translation: You can't spy on American citizens.
Section 1803(a)(2) requires that the Attorney General report to Congress (specifically, the House and Senate Intelligence Committees) about whether any American citizens were involved, what minimization procedures were undertaken to avoid it and protect their identities, and whether his actions comply with the law.