The top Senate Democrats on the Foreign Relations, Intelligence and Banking committees asked the inspectors general of three federal agencies Friday to launch formal probes into why President Trump has not fully implemented congressionally mandated sanctions against Russia.

“We are concerned about whether the sanctions implementation process within the administration is fulfilling CAATSA’s mandate and intent,” Sens. Robert Menendez (D-N.J.), Mark R. Warner (D-Va.) and Sherrod Brown (D-Ohio) wrote in a letter to the inspectors general for the State and Treasury departments and the intelligence community. The “CAATSA” acronym refers to a law Congress passed last August mandating sanctions against Russia, Iran and North Korea. In the time since, the Trump administration has designated entities to be hit with the new sanctions only once, the senators stressed — despite having taken other steps to identify entities engaging in activities that the law made sanctionable.

The senators challenged the inspectors general to determine whether Trump himself was the reason certain entities had avoided being designated for sanctions.

“It seems clear that several weeks ago, the administration had identified specific Russian entities that had played a role in supplying or otherwise supporting the government of Syria’s chemical weapons program, had prepared a list of such entities for sanctions designation, and Ambassador Nikki Haley publicly announced their imminent designation,” the senators wrote. “But then the administration did not designate them, reportedly at the direction of the President.”

It is not the first time that lawmakers, particularly Democrats, have questioned Trump’s motives regarding Russia, even as his administration has taken certain steps to rebuke Russia for its aggressive activities, including expelling dozens of Russian officers from the United States this spring. Much of that criticism has focused on the sanctions measures that became law last August, as the law carried a late January deadline for implementation, which the administration has missed.

But concerns about fully implementing Russia-related sanctions also have come from other corners of the Trump administration. Last month, Defense Secretary Jim Mattis warned the Senate Armed Services Committee that the United States’s ability to counter Russian military aggression would be compromised if there were no waivers to allow engagement with countries that had been historically dependent on Russian systems.

The three top Democrats also asked the inspectors general to examine “the internal processes by which your respective agencies have contributed to the creation of Russia sanctions designation packages,” as well as whether interagency issues created obstacles to implementing such measures.

Inspectors general are able to make their own determinations about investigations. But without any Republicans signing on to the senators’ letter, there is likely to be little pressure on the inspectors from the secretaries and other Cabinet-level officials in the Trump administration to delve into the matter.