President Donald Trump and Sen. Rand Paul (R-KY) remain rather unlikely allies. The two went tit-for-tat on the campaign trail, with Trump making pointed jabs about the Kentucky senator’s poll numbers and Paul mocking Trump as a power-hungry “rich guy from New York.” More recently, Paul helped scuttle a House vote on an Obamacare repeal bill, handing a huge embarrassment to the Trump administration.

This week, though, they’ve been brought together by a shared fixation on surveillance.

Paul has gone to bat for the President over reports that former President Barack Obama’s national security adviser, Susan Rice, requested the unmasking of U.S. persons in several intelligence reports that referenced Trump transition officials.

“I believe Susan Rice abused the system and she did it for political purposes. She needs to be brought in and questioned under oath,” he said Tuesday on MSNBC’s “Morning Joe.” “This was a witch hunt that began with the Obama administration, sour grapes on the way out the door. They were going to use the intelligence apparatus to attack Trump, and I think they did.”

Rice has denied any improper action, saying unmasking names of U.S. persons is sometimes necessary to understand the “context” for intercepted conversations. She also insisted that she leaked no information to the press.

National security experts say this sort of request is perfectly “appropriate” for a high-ranking official like Rice who is tasked with keeping tabs on foreign governments.

Paul isn’t buying it.

“DIRECTIVE FROM OBAMA?” he wrote in a Tuesday tweet linking to a Fox News article about his call for Rice to testify.

DIRECTIVE FROM OBAMA? Paul calls on Rice to testify over reports of unmasking request https://t.co/bnO0w8UKDM — Senator Rand Paul (@RandPaul) April 4, 2017

While conservative media and the Trump family have also been quick to jump on the Rice allegations, other Senate Republicans have mostly toed the line (with the exception of Sen. Tom Cotton [R-AR], who referred to Rice as the Obama administration’s “Typhoid Mary”).

Sen. John McCain (R-AZ) told CNN that “we have to have factual evidence” before alleging anything untoward about Rice’s requests.

McCain sits on the Senate Intelligence Committee, of which the Republican chair and Democratic vice-chair have vowed to conduct a thorough, bipartisan investigation into Russia’s interference in the U.S. election, including contacts between Trump staffers and Russian officials.

For Paul, a libertarian known for his attempts to filibuster John Brennan’s nomination as CIA director and the renewal of the Patriot Act, the Rice allegations are fresh fuel in his longstanding crusade against an omnipotent, expansive U.S. government surveillance program.

“For many years Senator Paul has been very vocal against the surveillance state and potential for abuse,” his communication director, Sergio Gor, said in a statement to TPM. “Regarding Susan Rice, he believes it needs to be fully investigated by Congress.”

Since arriving on Capitol Hill, Paul has been one of the loudest critics of the National Security Administration’s sweeping surveillance programs and often cautions Americans against “giving up their liberty.”

Despite Trump’s insistence that he was spied on by Obama administration officials, his administration has demonstrated little interest in loosening U.S. surveillance measures.

Backing the President on this particular allegation could be an opening for Paul to build goodwill with the Trump administration and gain its support for surveillance reforms down the line.

Paul said he discussed the need to reform U.S. intelligence activities while golfing with the President over the weekend.

“I may have given him my opinion on it,” Paul told a scrum of reporters.