Robert Satloff is executive director of the Washington Institute for Near East Policy, where Eric Trager is the Next Generation Fellow.

The raising of an al-Qaeda banner by the angry mob that breached the U.S. Embassy in Cairo on Tuesday — the anniversary of the Sept. 11, 2001, terrorist attacks — was disturbingly apt. Huge majorities in major Muslim countries prefer baseless conspiracy theories to the facts of what happened that other Tuesday morning 11 years ago. Although al-Qaeda routinely brags about its “achievement,” 75 percent of Egyptians, for example, still deny that Arabs carried out the attacks, as a Pew study reported in July 2011.

This denial of history has policy relevance for the United States: Mass rejection of the facts of 9/11 undermines U.S. global counterterrorism efforts. Persuading Muslims to set the record straight is a condition for any successful counterterrorism strategy.

President Obama rightly focused on this from his earliest days in office. In his 2009 Cairo address, the president denounced 9/11 revisionism in no uncertain terms. “I am aware that some question or justify the events of 9/11,” he said. “But let us be clear: al-Qaeda killed nearly 3,000 people on that day. . . . These are not opinions to be debated; these are facts to be dealt with.”

This month’s U.N. General Assembly meeting provides a critical test for the president’s commitment to combat such revisionism. The star of the sessions is likely to be Mohamed Morsi, Egypt’s new president. Obama reportedly plans to meet with Morsi, the popularly elected leader of the Arab world’s most powerful and populous state. But Morsi, a longtime leader of the Muslim Brotherhood, has not only evinced sympathy for the embassy attackers, he has also embraced some of the most vile conspiracy theories about 9/11.

Morsi has not been shy about airing his odious views. In a May 2010 interview with Brookings Institution scholar Shadi Hamid, Morsi dismissed al-Qaeda’s responsibility for the attacks. “When you come and tell me that the plane hit the tower like a knife in butter, then you are insulting us,” Hamid reported Morsi as saying. “How did the plane cut through the steel like this? Something must have happened from the inside. It’s impossible.” Similarly, in 2007, Morsi reportedly declared that the United States “has never presented any evidences [sic] on the identity of those who committed that incident.” In 2008, he called for a “huge scientific conference” to analyze “what caused the attack against a massive structure like the two towers.”

While Morsi has been silent about 9/11 since becoming president, the Brotherhood’s emergence over the past year as Egypt’s leading political force hasn’t moderated its “truther” rhetoric.

In a series of interviews in July, top Brotherhood leaders repeatedly denied al-Qaeda’s responsibility for the attacks. Mustafa Ghoneimy, leader of the Brotherhood’s Guidance Office, said “the Jews” had executed the attacks. “So many Jews worked in these two towers,” he said. “And on that day, they were off.” Meanwhile, Brotherhood secretary general Mahmoud Hussein pinned the attacks on “one of the intelligence services in America, or the Jews.” Spokesman Mahmoud Ghozlan speculated that “intelligence services” were behind the attacks, since “it is impossible for immature pilots to execute their ideas. It needs some professionalism to do it.”

To be sure, Morsi is not the first Egyptian ruler to trade in bigoted conspiracy theories. Then-President Gamel Abdel Nasser, the leader of secular pan-Arabism, once told a German interviewer that “no person, not even the most simple one, takes seriously the lie of the 6 million Jews that were murdered.” And the state television station of close U.S. ally Hosni Mubarak once aired during Ramadan a 41-part series based on “The Protocols of the Elders of Zion,” the infamous conspiracy screed of a Jewish cabal to control the world.

The Muslim Brotherhood’s 9/11 revisionism, however, coincides with the moment that Egypt’s ruling Islamists are going, hat in hand, to world capitals and international financial institutions. Egypt’s nearly bankrupt economy, decrepit institutions and declining domestic security situation have forced its leaders to seek help abroad. Yet the Brotherhood apparently believes that it can win support without adjusting its hateful rhetoric or ideology.

Washington has a broad range of interests in Egypt as it shifts from authoritarian to representative rule, ranging from security cooperation and regional peace to political pluralism and religious tolerance. The United States should be willing to extend economic and military aid to Egypt commensurate with the latter’s needs and its commitment to partner in advance of common objectives. But in working out the details of this new arrangement, our president should not give his personal imprimatur to leaders who espouse repulsive, abhorrent views that undermine a vital U.S. national security interest.

To that end, Obama should explicitly condition any meeting with Morsi on the latter’s clear and public renunciation of 9/11 revisionism. This position would present Morsi with a stark choice: He can either repudiate the hate-filled conspiracies that he has helped to sow and reap the benefits of Obama’s embrace, or he can expose himself as an irresponsible ideologue with whom few members of the international community will want to deal. Failure to lay down a marker with Morsi before he comes to New York means Morsi may never have to make that choice.