Colorado Sen. Mark Udall lost his seat on Tuesday, the Associated Press is projecting. He lost a hard-fought race against Republican challenger Rep. Cory Gardner.

The candidates sparred over a variety of the issues, from Obamacare to birth control. But the biggest impact of Udall's defeat could be on civil liberties.

Along with Sen. Ron Wyden (D-OR), Udall was the Senate's most dogged critic of the National Security Agency and the Central Intelligence Agency. The pair sat on the Senate Intelligence Committee, allowing them to keep tabs on those agencies' activities. Wyden's term runs through 2016.

Civil libertarians have been dreading the possibility of a Udall loss for months

In 2012, a year before Edward Snowden publicly revealed the extent of the NSA's domestic surveillance, Wyden and Udall issued a statement warning that the public would be "stunned" when they learned how the government was interpreting the Patriot Act. It's now believed these comments refer to the NSA's warrantless collection of every American's calling records.

And Marcy Wheeler, a civil libertarian who writes for the Empty Wheel blog, says Udall was the leading critic of the CIA's controversial torture programs. He has pressed for public disclosure of more information about those programs.

Civil libertarians have been dreading the possibility of a Udall loss for months. "It would be a significant loss for the movement," Laura Murphy of the American Civil Liberties Union told The Hill last month. "What Udall has is the institutional memory, and the relationships in the civil liberties community, in the Democratic Party and in the tech industry so that we don’t have to start over again with someone new."

Wheeler says she's optimistic about Gardner. "I think Gardner will be good on surveillance issues, but he won't get on the intelligence committee." That means that even if Gardner is as committed to civil liberties as Udall has been — which, judging from his ACLU rating, seems unlikely — he won't have the opportunity to shape civil liberties debates the way Udall has.

Some civil libertarians are experiencing a sense of deja vu tonight. Until 2010, the leading civil libertarian and NSA critic in the Senate was Sen. Russ Feingold (D-WI). But he lost his seat to a Tea Party Republican, Ron Johnson.

With Udall out, Wyden may have to look across the aisle for a legislative ally. Since his election in 2010, Sen. Rand Paul (R-KY) has often worked with Wyden and Udall on proposals to rein in NSA spying.

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