Rand Paul attempted to derail efforts to reauthorize bulk collection of American phone records in a dramatic showdown on Wednesday by taking over the floor of the Senate hours before a weekend deadline to renew the justification of the National Security Agency’s dragnet surveillance.

The Kentucky senator and Republican presidential candidate had pledged to filibuster any efforts to extend the lifespan of a key 2001 surveillance authority that the NSA has used since 2006 to collect Americans’ phone data in bulk. The Guardian exposed the dragnet in June 2013 thanks to whistleblower Edward Snowden.

A key provision of the Patriot Act, known as Section 215, is set to expire on 1 June, and the House of Representatives voted overwhelmingly last week to ban mass collection of Americans’ phone records by passing the USA Freedom Act – legislation that Mitch McConnell, the Republican Senate majority leader, staunchly opposes.

Although McConnell plans to bring the House-passed bill to the floor for a vote this week, he has doubted its passage in the Senate and is instead pushing for a two-month extension of the Patriot Act in its current form as an interim solution.

While it remained unlikely that Paul’s delaying tactics would succeed in blocking the Patriot Act, they raised pressure on McConnell given the limited time on the clock. Under a compressed schedule by a House that is slated to adjourn on Thursday until after Section 215 expires, McConnell has to not only bring surveillance legislation to the floor, but also a highway funding bill and trade promotion authority before Congress goes on recess until the beginning of June.

South Dakota senator John Thune, the third-ranking Republican in the Senate, told reporters that at least after its first several hours, Paul’s talkathon would not affect leadership’s plans to advance trade legislation and resolve differences over the Patriot Act.

“It’s just a reality we have to deal with. We’ve got people who are in different places,” said Thune, who also suggested that the House version of the USA Freedom Act lacked the 60 votes required to clear the Senate.

Thune’s comments came despite an effort by representatives Jim Sensenbrenner and Bob Goodlatte, the Republican co-authors of the House USA Freedom Act, to sell the bill to their colleagues in the Senate in a closed-door meeting on Wednesday. A number of Republicans who emerged from the meeting said they still preferred the two-month extension being pushed by McConnell, arguing that the House bill went too far in reigning in the agency’s capabilities.

“I do think that on this side of the building the vast majority of Republicans are very concerned about moving to something that we don’t know is going to work,” Republican Tennessee senator Bob Corker, who supports extending the Patriot Act as is, told the Guardian after the meeting. “[It’s] problematic certainly with the number of people that supported in the House. … No doubt it creates a conundrum.”

Paul also opposes the House-passed bill, but for the opposite reason – he has said the USA Freedom Act does not go far enough. Hours into his floor speech, Paul was still going strong, striding the floor behind his Senate desk to keep mobile and regaling the empty chamber with details of British and American constitutional history.

“The fight against general warrants was the spark that led to the American revolution; this is how important this is,” he said.

He also focused heavily on the counter-productive nature of the NSA’s activities, arguing mass surveillance made it harder to catch specific terrorist plots such as the Boston Marathon bombing.

“We spend so much time getting the haystack bigger and bigger, that they can’t find the needle because the haystack is too damn big,” said Paul.

“I didn’t come to the floor today because I want to get, you know, some money for one individual project, for one person. I came because I want something for everybody. I want freedom for everybody, and I want protection against the government’s invasion into your privacy.”

Allies in the fight against mass surveillance were also preparing to band together with Paul on the Senate floor. Oregon senator Ron Wyden, a Democrat and longtime critic of the NSA’s surveillance methods, was the first to join Paul in opposition to the Patriot Act. Utah senator Mike Lee, a Republican and Senate co-sponsor of the USA Freedom Act, also joined Paul on the Senate floor.

The White House also threw its weight behind reform efforts on Wednesday with several behind the scenes interventions.

One senior administration official told the Guardian that Congress was wrong to think that House members could safely vote on the re-authorisation when it returns on 1 June, arguing the sunset provision begins at midnight on 31 May.

The Obama administration, which supports the USA Freedom Act, also sent word to Capitol Hill via the Justice Department that it had barely 24 hours to resolve the impasse before it began mothballing its controversial domestic bulk phone data collection.

A memo sent on Wednesday by the administration warned that the NSA could find itself in legal jeopardy if it continued surveillance on Americans’ phone data after Thursday – what the Justice Department described as a prudential matter ahead of the looming expiration of the base legal authority for the program.

“After May 22, 2015, the National Security Agency will need to begin taking steps to wind down the bulk telephone metadata program in anticipation of a possible sunset in order to ensure that it does not engage in any unauthorized collection or use of the metadata,” states the memo, circulated on Capitol Hill and first reported by National Journal. The Guardian independently obtained a copy.

While the claimed legal authority for the program, Section 215 of the Patriot Act, expires on 1 June, the memo notes that the next 90-day order from a secret surveillance court necessary to gather the bulk data must be filed by Friday – after the House of Representatives, which has already voted overwhelmingly to stop the program, is in recess.

“For these reasons, after May 22, 2015, it will become increasingly difficult for the government to avoid a lapse in the current NSA program of at least some duration,” the memo states.

Over in the House, legislative aides denied that surveillance hawks could cobble together the necessary 218 votes to give the Patriot Act’s key surveillance provision a short-term extension that has become McConnell’s fallback gambit.

One aide told the Guardian that all legislative strategy on both sides of the debate would be scrambled if Section 215 of the Patriot Act expires. But the aide, who requested anonymity in order to discuss a swiftly moving process, said the Senate has no time to convince the House to do anything else on surveillance: “The House will be gone by lunchtime tomorrow,” with lawmakers rushing to airports to return to their constituents for a legislative holiday that will last until after the scheduled expiration of Section 215.

Aides to Senate Republican leaders argued otherwise, noting that the House will reconvene after recess on 1 June. If the House took up a short-term extension immediately upon their return, aides said, any lapse at midnight would have little real-world impact.