WHEN SHE met Jamal Khashoggi, Hatice Cengiz was a Turkish PhD student with little exposure to the United States and no interest in becoming a political activist. Yet last week she found herself in Washington, meeting with senior officials of the Trump administration and testifying to Congress. After Khashoggi was murdered by Saudi government agents last October, Ms. Cengiz, who was his fiancee, had hoped to grieve privately and remain out of the limelight. Yet a terrible truth has slowly become clear to her: The U.S. democratic institutions that Khashoggi had often praised to her are failing to hold the Saudi regime accountable.

“In the early days, President Trump said it would be solved,” Ms. Cengiz told a House subcommittee on Thursday. “Ms. Pelosi said how unacceptable it was. Seven or eight months later, we see that nothing has been done.”

The Trump administration has imposed sanctions on 17 Saudis it says were involved in the murder, and Congress passed legislation — vetoed by Mr. Trump — that would have ended U.S. support for the Saudi military intervention in Yemen. But the administration has defied a legally binding congressional request that it determine whether Saudi Crown Prince Mohammed bin Salman bore responsibility for the murder, and legislation that would punish the crown prince and his regime has stalled.

Ms. Cengiz pointed out that basic questions about the murder have yet to be answered. “We still do not know why he was killed,” she said of Khashoggi, a prominent journalist who contributed columns to The Post. “We don’t know where his corpse is.”

Though Secretary of State Mike Pompeo claims that the administration is still investigating the case, it’s obvious that Mr. Trump is determined to bury it. The problem with that policy is not just its moral depravity; it is also an invitation to Mohammed bin Salman and other despots to murder more journalists and other opponents. “If Jamal’s murder passes with impunity, then me speaking here today puts me in danger,” said Ms. Cengiz. “It places everyone who shares these universal values in danger.”

Congress still has an opportunity to act. Sen. James E. Risch (R-Idaho), chairman of the Senate Foreign Relations Committee, has been working on legislation that he hopes could pass Congress and escape Mr. Trump’s veto. To do so, it would omit direct sanctions on the crown prince and restrictions on U.S. arms sales. But if it conditions U.S. visas for the Saudi elite and their families on tangible reforms, including the release of political prisoners, it could prove useful. A bill in the House, sponsored by Rep. Tom Malinowski (D-N.J.), would require the director of national intelligence to provide Congress with a list of individuals responsible for Khashoggi’s death and deny them entry into the United States unless steps on human rights are taken.

Nothing Congress can do can erase Ms. Cengiz’s terrible loss. But it still has the chance to restore the hope that she and many others in the Middle East once had that the United States would not tolerate without consequence the murder and dismemberment of a critical journalist.