Senate Democrats want to know who at the National Security Council is in charge of responding to coronavirus and other challenges in global health security.

“Is NSC working to hire a dedicated, senior global health security expert?” asked 24 senators led by Elizabeth Warren of Massachusetts and Patty Murray of Washington, in a Thursday morning letter to National Security Adviser Robert O’Brien.

Warren, a 2020 presidential candidate, and Murray, the ranking member on the Health, Education, Labor and Pensions Committee had previously written to then-national security adviser John Bolton in May 2018 on the same topic after reports that the person in charge of global health at the National Security Council was departing as part of Bolton’s reshuffling of the operation.

Warren and Murray, now joined by 22 of their colleagues, indicated in their letter that the post might still be vacant. O’Brien serves as part of President Donald Trump’s coronavirus task force.

The latest letter was shared with CQ Roll Call ahead of formal release.

“But you are not a public health expert, and it is not clear if the NSC has such an expert in position to sufficiently advise or coordinate its global public health work on the Task Force and in other areas,” the senators wrote to O’Brien.

“Families concerned about the novel coronavirus threat need to know the NSC has a dedicated, senior official with appropriate expertise and authority to address the domestic and global health threats from the virus,” the 24 Democrats wrote. “It is of paramount importance that this person approaches this role through a public health lens.”

The letter comes after O’Brien said at an Atlantic Council event Tuesday that, “we just don’t know” about the origins of the coronavirus within China. He made the observation in response to a question about comments from Sen. Tom Cotton, R-Ark., that had raised the possibility of the virus coming from a Chinese laboratory.

The Centers for Disease Control and Prevention has suspected the virus originated in animals and made the leap to humans.

CDC Deputy Director Anne Schuchat said earlier this week that the virus development appeared to be, “quite consistent with emergence from animal to human acquisition.”

The Democratic senators are seeking responses by Feb. 27 from O’Brien to a series of questions, including interagency coordination between the National Security Council and CDC and other public health agencies.