Lawmakers are already justifying their votes for making major changes to that proven regime by saying that the bill is a reasonable compromise that updates FISA technologically and will make it somewhat harder to spy on Americans abroad. But none of that mitigates the bill’s much larger damage. It would make it much easier to spy on Americans at home, reduce the courts’ powers and grant immunity to the companies that turned over Americans’ private communications without a warrant.

It would allow the government to bypass the FISA court and collect large amounts of Americans’ communications without a warrant simply by declaring that it is doing so for reasons of national security. It cuts the vital “foreign power” provision from FISA, never mentions counterterrorism and defines national security so broadly that experts think the term could mean almost anything a president wants it to mean.

Supporters will argue that the new bill still requires a warrant for eavesdropping that “targets” an American. That’s a smokescreen. There is no requirement that the government name any target. The purpose of warrantless eavesdropping could be as vague as listening to all calls to a particular area code in any other country.

The real reason this bill exists is because Mr. Bush decided after 9/11 that he was above the law. When The Times disclosed his warrantless eavesdropping, Mr. Bush demanded that Congress legalize it after the fact. The White House scared Congress into doing that last year, with a one-year bill that shredded FISA’s protections. Democratic lawmakers promised to fix it this year.

Democratic Senators Patrick Leahy, Russ Feingold, Christopher Dodd and Jeff Bingaman plan to offer amendments to do that, but there is little chance they will pass. The Senate should reject this bill and start over with modest legislation that makes the small needed changes and preserves Americans’ fundamental protections.