Russian tourists at Sharm el-Sheikh airport, in Egypt, on Friday. (Khaled Elfiqi/European Pressphoto Agency)

THE CRASH of a Russian airliner in the Sinai Peninsula last week posed an immediate test for Russia, whose citizens made up most of the 224 killed, and for Egypt, which is responsible for security at the beach resort of Sharm el-Sheikh, where the flight originated. So it says much about the autocratic regimes that control the two countries that the first word that the destruction of the aircraft might have been a terrorist attack — and the first measures to protect the tens of thousands of tourists still in the Sinai — came from the government of Britain.

Prime Minister David Cameron, saying it was “more likely than not” that “a terrorist bomb” had destroyed the airliner, suspended regular British flights to Sharm el-Sheikh while taking steps to bring home some 20,000 British tourists stranded there. The governments of Vladi­mir Putin in Moscow and Abdel Fatah al-Sissi in Cairo reacted indignantly. While Mr. Putin suspended Russian flights on Friday, his spokesman was still insisting there was no reason to conclude that there had been an act of terrorism. When not issuing his own denials, Egypt’s transport minister was obstructing the British evacuation effort, reducing the number of London flights from 29 to eight .

While Western governments worried about protecting their citizens, the Sissi and Putin regimes were focused on defending themselves. Both rulers have sold themselves as warriors courageously taking on the Islamic State and its affiliates; both are using that fight as a pretext to accomplish other ends, such as repressing peaceful domestic opponents and distracting attention from declining living standards. On the actual battlefield, both are failing: Mr. Sissi has been unable to pacify the Sinai in two years of scorched-earth operations, while Mr. Putin’s offensive against rebels fighting the regime of Bashar al-Assad in Syria has quickly bogged down.

As U.S. officials underlined, there are strong indications but so far no conclusive evidence that the plane was bombed. Yet to concede that the Islamic State might have penetrated Egyptian security at the Sharm el-Sheikh airport, and that Mr. Putin’s Syrian ad­ven­ture could have prompted the worst civil air attack in Russia’s history, would be not just an embarrassment but a potentially grievous political wound. So the two regimes are turning to familiar tactics: bluster and obfuscation. Mr. Sissi told the BBC that suggestions of terrorism must be intended “to damage the stability and security of Egypt and the image of Egypt.” Russian officials, who still deny the overwhelming evidence that a Russian anti-aircraft missile downed a Malaysian airliner over Ukraine last year, are insisting that it will take months to draw any conclusions. .

The state media controlled by Messrs. Putin and Sissi have a nasty habit of blaming all disasters on the United States, no matter how far-fetched the theory required. So we won’t be surprised if Russians and Egyptians are told the CIA is somehow responsible for the tragedy in the Sinai. Those seeking a more rational conclusion must consider this somber point: The Egyptian and Russian regimes are far less adept at fighting terrorism than they are at lying.