MUSTAFA KASSEM, an auto-parts dealer from Bethpage, N.Y., was visiting his native Egypt in August 2013 when he and his brother-in-law were stopped by a military patrol outside a shopping mall where they had been exchanging money. When the soldiers demanded the men’s papers, Kassem, an American citizen, displayed his blue U.S. passport. That, it turned out, was a fatal mistake. “They allowed my brother-in-law to pass,” Kassem recounted in a letter to President Trump. “But I was treated differently. I was an American.”

Kassem was arrested, badly beaten and locked up in the notorious Tora prison. On Monday, after more than six years of unconscionable mistreatment by Egyptian authorities, the 54-year-old father of two died. His only offense was to be a U.S. citizen in a country that receives $1.4 billion in annual U.S. aid — whose ruler, Abdel Fatah al-Sissi, has been called “my favorite dictator” by Mr. Trump.

The president has bragged about his successes in freeing Americans held abroad. In this case, the administration’s failure was abject. Vice President Pence raised Kassem’s plight with Mr. Sissi in January 2018, after he had been held for 4½ years without trial. There was no result. In December, with Kassem’s health in peril after 15 months on a hunger strike, Secretary of State Mike Pompeo brought him up in a discussion with Egypt’s foreign minister. Again, Cairo ignored the appeal.

What’s particularly striking is that the regime never offered any evidence whatsoever that Kassem had committed an offense. When he was finally brought to court, in September 2018, he was included in a mass show trial of 738 defendants. No individualized evidence was ever presented against him. Yet he was sentenced to 15 years.

Perhaps Kassem was kept in prison because the regime did not want to acknowledge that the soldiers who responded to his U.S. passport by beating and arresting him had acted wrongly. Perhaps he was seen as a useful subject for regime propaganda, according to which American “spies” are seeking to destabilize the country. We don’t know, and the Trump administration doesn’t know, because Mr. Sissi and his jailers never offered a credible explanation.

Far from earning protection through his U.S. citizenship, Kassem was subjected to shocking mistreatment. Though he was a diabetic with a heart condition, authorities restricted his access to medication throughout his imprisonment. Yet Mr. Trump has had nothing to say about this deadly abuse by a nominal ally. The only administration comment to date came from the assistant secretary of state for Near Eastern Affairs, David Schenker, who said Kassem’s death was “needless, tragic and avoidable,” but did not assign responsibility for it.

Congress anticipated cases such as this when it passed the Magnitsky Act, named for a Russian lawyer who was persecuted by the government of Vladi­mir Putin and died in prison. It provides for the sanction of all officials complicit in such human rights crimes, and it allows members of Congress to initiate cases by asking the administration to investigate. Kassem’s case cries out for such action.

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