WASHINGTON — Democratic senators are urging President Donald Trump to keep the door open to refugees as his administration, which has already pushed the number admitted to an historic low, weighs imposing unprecedented restrictions on the number of refugees allowed in the U.S.

In a letter obtained by NBC News, the 10 Democrats on the Senate Foreign Relations Committee warned Secretary of State Mike Pompeo about possible damage to America's diplomatic clout and strategic interests around the world from any further reduction in refugee admissions.

The Trump administration last year set the lowest ceiling ever for refugees allowed to resettle in the U.S., limiting the number to 45,000 — and then admitted even fewer. After decades of bipartisan support for much higher numbers, said the senators, "We are concerned about the foreign policy and national security impact of any further downward retreat on admission numbers."

The letter coincides with an internal debate inside the Trump administration about the cap for refugee admissions for the next fiscal year, with civil servants at the State Department and military officers at the Pentagon pitted against political appointees who favor drastically curtailing the number of refugees permitted into the country.

An average of 95,000 refugees have been admitted to the U.S. annually since the Refugee Act of 1980 was adopted. Republican presidents Ronald Reagan and George H.W. Bush set the highest cap for refugees, at 140,000 and 142,000, the letter said.

By taking in refugees fleeing war and persecution, the lawmakers wrote in their letter to Pompeo, the U.S. has shown moral leadership, set an example for other Western countries and bolstered ties with allies and partners facing humanitarian crises.

"Refugee resettlement helps foster regional stability, assists close allies such as Jordan, and is a diplomatic tool for securing greater humanitarian engagement from other wealthy nations. Refugee resettlement has proven to be an important tool in our foreign policy toolkit," said the letter.

The State Department did not immediately offer an on-the-record comment on the letter.

Trump senior policy adviser Stephen Miller has led the effort to limit the admission of refugees, arguing that they represent a potential security threat and an economic burden. He and other immigration hawks also maintain that the government lacks the capacity to vet larger numbers of refugees as manpower has been shifted to managing a vast backlog of asylum seekers.

Democrats in Congress and humanitarian organizations reject the rationale for cutting back on refugees, saying it jeopardizes relations with governments such as Jordan or Bangladesh that are overwhelmed by civilians pushed out of their home countries by war and violent extremism. They also argue that administration officials could find the manpower needed to handle refugee cases if they had the political will and that the White House has often overstated the security threat posed by refugees without firm evidence or intelligence assessments.

Sen. Bob Menendez of New Jersey, the ranking Democrat on the Senate Foreign Relations Committee and a sharp critic of the administration's immigration and refugee policies, told NBC News in an email he hoped Pompeo would be "willing to be a voice of reason in the room when President Trump is told he should continue grinding the U.S refugee program to a halt."

Menendez added, "Having surrounded himself with nativists and xenophobes as senior advisors, I have no doubt President Trump will continue to be counseled against policies that uphold our nation's humanitarian duty of providing those escaping persecution the opportunity to seek protection and safe haven."

Although the ceiling for refugee admissions for this fiscal year is at a historic low of 45,000, the number of refugees actually being admitted is drastically lower. If current trends continue, only about 20,000 to 21,000 refugees will allowed into the country by the end of September, less than half the official cap.