WASHINGTON — A group of 10 Democratic senators have issued a new letter blasting Defense Secretary Mark Esper for “dysfunctional decision-making” in how the Pentagon has tackled the coronavirus pandemic — with the Pentagon offering unusually strong pushback.

In it, the senators express “grave concern” about how Defense Department leadership has handled the disease, writing: “Civilian leadership of the Department has failed to act sufficiently quickly, and has often prioritized readiness at the expense of the health of servicemembers and their families. This failure has adversely affected morale, and, despite the Department’s best intentions, undermined readiness.”

The letter was signed by Senate Armed Services Committee members Elizabeth Warren of Massachusetts and Mazie Hirono of Hawaii, as well as Kamala Harris of California, Patty Murray of Washington, Richard Blumenthal of Connecticut, Jeff Merkley of Oregon, Sherrod Brown of Ohio, Ron Wyden of Oregon, Amy Klobuchar of Minnesota, and Ed Markey of Massachusetts.

Warren, Harris and Klobuchar were all candidates for the Democratic presidential nomination during the 2020 race, and Warren and Harris are each considered potential picks as vice president for expected nominee Joe Biden.

In the letter, the senators question Esper’s “dangerous misunderstanding” of COVID-19, citing comments he made April 16 indicating he had just learned that the disease can be carried by asymptomatic individuals, something well-known publicly for months. The senators also attacked his “tentative approach” to giving guidance to military commanders, which has “put recruits and recruit training staff at risk.” The lawmakers also warned that a decision “not to share installation-specific COVID data has sowed fear within both military and civilian communities.”

The letter represents a level of formal criticism that Esper has largely avoided through his first 10 months as defense secretary. Even in situations where Democrats have criticized a department policy, such as moving congressionally appropriated funding away from the department and toward the border wall with Mexico, the target of attacks have primarily been the White House and not Esper.

With the Senate set to return next week following its coronavirus-caused break, Esper may find himself facing tougher criticism in person, which could also reverberate as the Defense Department seeks to secure its portion of the $740 billion national security budget request.

The letter also requested a response to a series of questions by May 11, focused on what the department’s long-term plan is to deal with the virus, which is projected by experts to have another resurgence in the coming winter.

In an unusual response to such Congressional letters, the department released an almost 700 word statement from chief spokesman Jonathan Hoffman saying the senators “cherry-picked false and repeatedly debunked assertions that do not reflect reality.”

Hoffman’s statement largely focuses on the accusations Esper has not given clear enough guidance, reiterating previous comments from the secretary that it is not realistic to give guidance from the top that would work for every situation that the military may find itself in. The statement also highlights the work the department has done to combat the disease, including the use of hospital ships and securing medical supplies.

“Above all, we have attempted to be open, receptive and responsive to the American people and their elected representatives," Hoffman said. "While we are not above criticism, this letter does not even remotely accurately reflect our record of action against the Coronavirus and the great lengths we have gone to protect our people. We look forward to continuing to discuss the lessons learned from this outbreak and our path forward with our highly informed and engaged oversight committees.”

Updated 3:37 PM EST with Hoffman’s statement.