The current New York City mayor, Zohran Mamdani, has affronted one of his predecessors, Rudy Giuliani, by taking the inflammatory step of deciding to attend the city’s 9/11 commemoration. “It offends me,” Giuliani proclaimed earlier this week on Newsmax.One might suspect that the nature of Mamdani’s offense lay in his being a politician who is associating himself with a day that Giuliani prefers to associate with Giuliani. But the former mayor proceeded to lay out a much darker rationale. “They’re taking over certain parts of America and certain parts of Europe. They have every desire to take us over. This is not ‘they want to be just another religion,’” he said of Muslims. “Mamdani is a clear, a clear supporter of that. All of the Muslims he supports are murderers!”Like many of Giuliani’s utterances, this one has no connection to reality. Yet his assertion that Mamdani harbors some secret desire to conquer the United States in the name of Islam, that his religion is the skeleton key to a web of sinister motivations, is now treated on the right as almost banal. A quarter century after 9/11, delirious anti-Muslim bigotry is almost routine in the political rhetoric of many conservatives.The conventional account of Donald Trump’s political career explains his rise to power as a populist revolt against Republican orthodoxy. The GOP elite had lost touch with their base by endorsing immigration reform, free trade, or forever wars in the Middle East, which created an opening that Trump exploited.[Read: What the Islamophobic attacks on Mamdani reveal]That story is largely true, but it misses an important issue. The President George W. Bush–era Republican Party after 9/11 insisted that the United States was at war not with a religion but with an idea. America opposed radical Islamism, not Islam. We stood for freedom as a universal human principle.Not all voters on the right accepted this formulation. Some believed that the United States was at war with Islam itself. By 2007, conservative Republicans viewed Islam negatively by a margin of more than 30 points; Democrats, independents, and moderate Republicans all held net-favorable views. Ten years later, nearly 80 percent of Republicans believed that the values of Islam were at odds with American values. One of the most important and ominous notions that Trump has seized upon and legitimized is that Muslims are inherently un-American.Anti-Muslim sentiment sprang up organically in the immediate aftermath of the 9/11 attacks, but Bush’s forceful defense of pluralism confined it to the rantings of Ann Coulter, Michael Savage, and other fringe reactionaries. After Coulter called on the United States in 2001 to “invade their countries, kill their leaders and convert them to Christianity,” National Review dropped her column. As Bush passed from the scene and was replaced by Barack Obama, some right-wing-outrage entrepreneurs recognized an opportunity to redefine the War on Terror as a war against Islam.Trump himself was among the first to see the opening. In 2010, a right-wing backlash arose in opposition to a proposal for a Muslim cultural center, modeled on the YMCA or a Jewish community center, in downtown New York. The most hysterical opponents depicted the center, which planned to call itself Park51, as a “victory mosque” celebrating the destruction of the World Trade Center. Other conservatives merely insisted that it was “insensitive” for Muslim Americans to open a center in the general neighborhood of Ground Zero.Trump inserted himself into the controversy, proposing that he purchase the property to halt construction on the putatively offensive site. In his offer letter (which, naturally, he made public), Trump called it a “very serious, inflammatory, and highly divisive situation that is destined, in my opinion, to only get worse.” David Letterman asked him, “Does this, in fact, suggest that we are officially at war with Muslims?” Trump, who was still in the formative stage of his transition from celebrity to right-wing rabble-rouser, replied, “Well, somebody knocked down the World Trade Center.” He later added, “Somebody’s blowing us up. Somebody’s blowing up buildings, and somebody’s doing lots of bad stuff.”Trump’s first campaign was pockmarked with undisguised bigotry against Muslims. He falsely claimed that Muslims in New Jersey had cheered the 9/11 attacks en masse, and he called for surveillance of mosques, a database of Muslims in America, and a ban on Muslims entering the United States. He associated the sitting president with Islam by incessantly using his middle name.He has continued to attack Muslims as disloyal or un-American. He falsely claimed that Representative Ilhan Omar of Minnesota, a Democrat, had praised al-Qaeda, and he demanded that she and Reprepresentative Rashida Tlaib of Michigan, both of whom are U.S. citizens, be sent “back from where they came.” He insinuated that Mamdani has no right to reside in the United States: “A lot of people are saying he’s here illegally.”The through line connecting these smears is the assumption that Muslims cannot be Americans, even if they arrive legally, even if they are born here. Trump has made this point explicitly and told Sean Hannity in 2016, “Assimilation has been very hard. It’s almost—I won’t say nonexistent, but it gets to be pretty close. And I’m talking about second- and third-generation. They come—they don’t—for some reason, there’s no real assimilation.”This sort of rhetoric has grown so common that episodes such as the uproar against Mamdani have come to feel like normal politics, rather than paranoia and rank discrimination. The New York Post alone has published at least eight stories (as of press time) hyping the Giuliani-fueled controversy.Some relatives of 9/11 victims have claimed that Mamdani’s presence at the observance would be a distraction (even though mayoral attendance has been a regular feature throughout its existence). Others have depicted their anger as a protest against Mamdani’s current agenda. “It’s not about his religion or where he came from. It’s about the policies he has today,” one explained. Is it the plan for free buses? The pied-à-terre tax?[Asma Khalid: Islamophobia has corroded American values]That Mamdani wishes to attend the ceremony and has denounced the 9/11 attacks as heinous terrorism ought to serve as satisfactory evidence that, whatever shortcomings he may have, he is not a supporter of al-Qaeda. Indeed, it might well be offensive if Mamdani did not want to attend the ceremony. The New York Post would need to publish phone-book-size editions to convey its full outrage.The logic of Islamophobia rejects out of hand that it is possible for Mamdani to oppose terrorism. 9/11 was, in this view, a battle in a war against Islam, so he is, by dint of his faith, the enemy. Thus, his desire to commemorate the tragedy, like Muslims’ desire to have a YMCA of their own in New York City, must be understood as revealing hidden malevolence.If you had asked Bush after 9/11 to imagine a future within his lifetime in which New York had a Muslim mayor who would join the city in mourning the attacks, he’d surely have considered it the ultimate vindication of the ideals he sought to foster. But Republicans have rejected Bush’s understanding of 9/11 and its meaning in favor of Trump’s.The events of the past decade, and especially the past six months, have clarified that the primary grounds for this repudiation does not seem to be Trump’s abhorrence for wars of choice in the Middle East. It is that Bush denied and suppressed contempt for Muslims, while Trump has honored and nurtured this hatred.*Image sources: Christy Bowe / Getty; Jim WATSON / AFP / Getty; Michael M. Santiago / Getty; Chip Somodevilla / Getty.