As Puerto Rico Gov. Ricardo Rosselló travels to Washington to meet with President Donald Trump on Thursday, a group of Senate Democrats is asking the administration about the accuracy of the island territory’s death toll.

Thirteen senators, led by Elizabeth Warren of Massachusetts, have written a new letter to acting Homeland Security Secretary Elaine Duke expressing concern that reports about morgues at Puerto Rican hospitals being full may signal that the official tally of 48 fatalities may be incomplete.

“An accurate death toll is important for understanding the true severity of the situation on the ground, for recognizing potential problems and vulnerabilities, for assessing the quality of the disaster response so far, and for setting policy going forward,” the senators wrote.

Four weeks since Hurricane Maria battered Puerto Rico, more than 80 percent of residents remain without electricity, according to the Federal Emergency Management Agency. Access to fresh food, clean water and medicine remains scarce in many parts of the island. 

Warren was joined by her colleague from Massachusetts, Sen. Edward J. Markey, along with members of the Senate Democratic conference from across the country in signing the letter to Duke.

They wrote they were echoing concerns previously raised by Democratic Reps. Bennie Thompson of Mississippi and Nydia Velázquez of New York.

Thompson is the top Democrat on the House Homeland Security Committee, and Velázquez was born in Puerto Rico.

“The aftermath of the hurricane continues to pose a mortal danger to many people on Puerto Rico,” the senators wrote. “There are concerns about dengue, chikungunya, and Zika. Puerto Ricans have been obtaining water from a contaminated Superfund site.”