More than 90 top American experts in atomic sciences, including a designer of the hydrogen bomb, publicly threw their weight behind the Iran nuclear agreement on Monday, exhorting Congress to preserve the accord in the face of President Trump’s disavowal of it.

In a letter to Senate and House leaders of both parties that emphasized the “momentous responsibilities” Congress bears regarding the agreement, the scientists asserted that the accord was effective in blocking Iran’s pathways to a nuclear weapon.

“Congress should act to ensure that the United States remains a party to the agreement,” read the letter, signed by what amounted to a who’s who of prominent physicists and other luminaries in American science.

The letter said the signers were offering their perspective “as scientists who understand the physics and technology of nuclear power, of nuclear explosives, and of long-range missiles; and who collectively bring their experience with nuclear nonproliferation.”