Three Democratic senators are calling for an investigation into "Project Airbridge," the Trump administration's public-private arrangement with six of the country's largest medical supply companies to deliver personal protective equipment (PPE) from overseas to the front lines of the COVID-19 pandemic.

Sens. Elizabeth Warren (D-Mass.), Richard Blumenthal (D-Conn.) and Senate Minority Leader Charles Schumer (D-N.Y.) said the initiative has lacked critical oversight and has misspent tens of millions of taxpayer dollars.  

"Project Air Bridge - like the broader Trump Administration response to coronavirus - has been marked by delays, incompetence, confusion, and secrecy involving multiple Federal agencies and actors," the senators wrote to the Pandemic Response Accountability Committee in a letter released Tuesday requesting that the panel initiate an investigation.

"Taxpayers have shelled out tens of millions of dollars on this secretive project and they deserve to know whether it actually helped get critical supplies to the areas most in need," the Democrats wrote.

Project Airbridge was led by President Trump's son-in-law and senior adviser Jared Kushner, and was touted by the administration as a historic and successful effort to ease critical shortages of PPE during the height of the pandemic.    

Under the arrangement, the federal government paid to fly the supplies to the U.S., so long as the companies agreed to sell at least 50 percent of the supplies to hot spots designated by the Centers for Disease Control and Prevention. The companies were allowed to sell the rest to anyone they wanted, at taxpayer expense.

The effort came under intense scrutiny from federal and state lawmakers who demanded answers from the administration about how the supplies were being distributed, and whether the White House was making distribution decisions based on politics rather than public health. Critics have seized on Kushner's role as well.

The administration wound down the effort last month after spending $91 million. But the impact on the U.S. pandemic response is unknown, as the White House, the Federal Emergency Management Agency and the companies involved have declined to disclose details about which supplies have been delivered and where.

The senators opened their own investigation in April, but the letter released Tuesday said they still lacked insight into key aspects of Project Airbridge, including the availability of supplies and their pricing.

The price of PPE shipped as a result of the program was supposed to be kept "reasonable," but in response to the senators' initial letters, the distributors said they were not aware of any effort by the Trump administration to track the pricing of PPE.

“It is not clear if the project was effective or cost-efficient, or if other alternatives — such as the early invocation and use of the Defense Production Act to produce medical supplies — would have better alleviated the PPE shortage, saved money, and saved lives,” the senators wrote.