On Thursday, President Donald Trump blasted Barack Obama‘s administration for a waiver it issued that would have authorized Iran’s government to temporarily wire money through an American bank, and called on federal investigators like special counsel Robert Mueller to look into the matter.

Trump Says Mueller Should Investigate Obama

“The Obama Administration is now accused of trying to give Iran secret access to the financial system of the United States. This is totally illegal,” Trump said in a tweet. “Perhaps we could get the 13 Angry Democrats to divert some of their energy to this ‘matter’ (as Comey would call it). Investigate!”

Republican lawmakers found out about the waiver in question, issued in early 2016, while investigating the Iran nuclear deal, which the U.S. has now pulled out of after Trump called the pact Obama helped reach “one of the worst” and most “one-sided” deals in history. The waiver was meant to permit Iran’s government to access money from an Omani bank “by converting them first to U.S. dollars and then to Euros,” according to Politico.

GOP officials maintained that this waiver broke a promise from the Obama administration that Iran would never be authorized access to U.S. financial markets. Former Obama administration members  have responded by saying this one-time waiver was simply part of the negotiations that ultimately led to the Iran deal. Gas prices in the U.S. have increased in the aftermath of the U.S.’s withdrawal from the Iran deal, a move that drew rebuke both in the U.S. and abroad. Trump claimed the deal failed to address all of Iran’s nuclear capabilities. The president’s latest claim could also be an attempt by him to divert attention away from Mueller’s Russia probe.

Even though Mueller is a Republican — as is former FBI Director James Comey — Trump has repeatedly claimed the special counsel is biased toward Democrats. In mocking Comey by calling the Iran waiver issue a “matter,” Trump was referencing the former FBI Director’s description of the bureau’s probe into Hillary Clinton‘s use of a private email server before the 2016 election.