An effort to block law enforcement officials from seizing emails older than 180 days without a warrant has twice won unanimous support in the House of Representatives, yet sponsors are struggling to remain optimistic.

That's because the reform has been blocked by unexpected poison-pill amendments and opaque conference committee decisions, tempering expectations despite apparent overwhelming support.

"I don't know that this bill will ever get a vote in the Senate. It’s almost too popular to get a vote [because] other legislators want to attach things to it," said Rep. Kevin Yoder, R-Kan., the lead House sponsor of the Email Privacy Act.

Authorities in most places can seize older emails from companies without showing a judge evidence of potential crimes, as is needed when authorities seize physical letters.

“There are thousands of Americans who have been spied on, and they don’t even know it,” Yoder said. “The IRS for a long time had a policy that it was OK to read Americans’ emails without their knowledge, without their permission, simply by sending a subpoena or a notice to an email provider, because that was within the powers of the government. And how would you ever know?"

A House-passed version of the Email Privacy Act awaits action by the Senate Judiciary Committee, and a large spending-bill amendment targeting the Internal Revenue Service and the Securities and Exchange Commission is likely to be included in the House version of an omnibus package later this year.

The IRS says it requests a warrant for emails as a matter of policy, but in recent years, both the IRS and the SEC have sought emails without one.

Debate about protections for email is part of a broader legislative and judicial struggle over how to apply the Constitution’s Fourth Amendment, which bars warrantless searches, to the internet and electronic devices.

“It’s a matter of time before it’s enacted either through a Supreme Court ruling or an act of Congress," Yoder predicted.

In recent decisions, the Supreme Court has protected cellphones of arrested people from warrantless search, and barred warrantless tracking of suspects’ movements with a GPS device. The Supreme Court is considering historical cell-site location data.

In four states — Ohio, Kentucky, Michigan, and Tennessee — authorities must obtain a warrant in order to seize older emails from providers, based on the U.S. Court of Appeals for the Sixth Circuit's 2010 ruling in U.S. v. Warshak that the Fourth Amendment applies.

Most fights over government access to communications pit a coalition of libertarian, conservative, and progressive lawmakers against centrists and party leaders deferential to executive-branch claims of national security. But Yoder’s push has taken on a different character, with little to no apparent opposition.

In the House, the Email Privacy Act passed unanimously in a recorded vote in 2016 and without opposition in a 2017 voice vote. A version was attached at least twice to omnibus bills that passed the House, before being stripped in leadership-negotiated conference committees, Yoder said.

In 2016, the standalone bill failed in the Senate Judiciary Committee, where Senate Majority Whip John Cornyn, R-Texas, sought to attach what backers viewed as a poison-pill amendment. It would have adopted language allowing the FBI greater warrantless access to Internet metadata including user browsing data.

Cornyn’s office did not comment on his intentions for the amendment that sank the bill in 2016, but the Email Privacy Act’s lead sponsor in the Senate, Mike Lee, R-Utah, isn’t optimistic.

“It's something where we would love Cornyn not to be opposed to it, but we don’t see a good possibility of anyone changing their minds anytime soon,” said Lee's communications director, Conn Carroll. “It’s probably not going to be called up anytime soon.”

A spokesperson for Senate Judiciary Committee Chairman Chuck Grassley, R-Iowa, didn’t respond to a request for comment.

The Email Privacy Act is supported by many outside groups, including the Heritage Foundation, the American Civil Liberties Union, and the Chamber of Commerce, along with companies that provide email services, such as Google.

Yoder said he has spoken to Cornyn about the bill, and Yoder views the bill's failure as emblematic of a dysfunctional legislative system, rather than opposition, though he suspects Attorney General Jeff Sessions and the SEC would object to limits on investigative powers.

“It speaks to a larger problem in Congress in which if you do what the founders intended, which is draft legislation, work it through the committee, and pass it through one body unanimously, then the other chamber knows they can utilize the good will of that bill to attach something that’s not as popular,” he said. "This is apparently the way things have gone on for all time."