Sen. Marco Rubio (R-FL) on Monday sent a letter to Attorney General William Barr about an issue he made former Attorney General Jeff Sessions aware of. Rubio believes Secretary of State John Kerry's actions relating to the Iran nuclear deal violated the Logan Act, which prohibits unauthorized people from negotiating with foreign governments.

"The American people deserve to know that U.S. laws are enforced regardless of any individual's past position. The Department of Justice should therefore make a determination on whether or not former Secretary of State John F. Kerry's recent actions related to the Joint Comprehensive Plan of Action (JCPOA) with Iran potentially violate the Logan Act or the Foreign Agents Registration Act," Rubio wrote.

In his September 18th letter to Sessions, Rubio cited Kerry's public meetings and phone calls with Iranian foreign minister Javad Zarif, German President Frank-Walter Steinmeier, European Union official Federica Mogherini and French President Emmanuel Macron. All of those meetings and phone calls took place after Kerry left office.

"As you know, the Logan Act is a statute that imposes consequences against any U.S. citizen who, 'without authority of the United States, directly or indirectly commences or carries on any correspondence or intercourse with any foreign government or any officer or agent thereof, with intent to influence the measures or conduct of any foreign government or of any officer or agent thereof, in relation to any disputes or controversies with the United States, or to defeat the measures of the United States,' Rubio wrote. "And the Foreign Agents Registration Act, as described by the Justice Department, is 'a disclosure statute that requires persons acting as agents of foreign principals in a political or quasi-political capacity to make periodic public disclosure of their relationship with the foreign principal, as well as activities, receipts and disbursements in support of those activities.'"

Here's the full letter: