Donald Trump utters plenty of ugly untruths: that undocumented Mexican immigrants are “rapists,” that Syrian refugees are committing “all sorts of attacks” in Germany and represent a “Trojan Horse” for ISIS. But he tells ugly truths too: that “when you give [politicians money], they do whatever the hell you want them to do.” And that “the Middle East would be safer” if Saddam Hussein and Muammer Qaddafi were still in power.

His latest ugly truth came during a Bloomberg TV interview last Friday, when he said George W. Bush deserves responsibility for the fact that “the World Trade Center came down during his time.” Politicians and journalists erupted in indignation. Jeb Bush called Trump’s comments “pathetic.” Ben Carson dubbed them “ridiculous.”

Former Bush flack Ari Fleischer called Trump a 9/11 “truther.” Even Stephanie Ruhle, the Bloomberg anchor who asked the question, cried, “Hold on, you can’t blame George Bush for that.”

Oh yes, you can. There’s no way of knowing for sure if Bush could have stopped the September 11 attacks. But that’s not the right question. The right question is: Did Bush do everything he could reasonably have to stop them, given what he knew at the time? And he didn’t. It’s not even close.

When the Bush administration took office in January 2001, CIA Director George Tenet and National Security Council counterterrorism “czar” Richard Clarke both warned its incoming officials that al-Qaeda represented a grave threat. During a transition briefing early that month at Blair House, according to Bob Woodward’s Bush at War, Tenet and his deputy James Pavitt listed Osama bin Laden as one of America’s three most serious national-security challenges. That same month, Clarke presented National Security Adviser Condoleezza Rice with a plan he had been working on since al-Qaeda’s attack on the USS Cole the previous October. It called for freezing the network’s assets, closing affiliated charities, funneling money to the governments of Uzbekistan, the Philippines and Yemen to fight al-Qaeda cells in their country, initiating air strikes and covert operations against al-Qaeda sites in Afghanistan, and dramatically increasing aid to the Northern Alliance, which was battling al-Qaeda and the Taliban there.

But both Clarke and Tenet grew deeply frustrated by the way top Bush officials responded. Clarke recounts that when he briefed Rice about al-Qaeda, “her facial expression gave me the impression that she had never heard the term before.” On January 25, Clarke sent Rice a memo declaring that, “we urgently need…a Principals [Cabinet] level review on the al Qida [sic] network.” Instead, Clarke got a sub-cabinet, Deputies level, meeting in April, two months after the one on Iraq.

When that April meeting finally occurred, according to Clarke’s book, Against All Enemies, Deputy Defense Secretary Paul Wolfowitz objected that “I just don’t understand why we are beginning by talking about this one man, bin Laden.” Clarke responded that, “We are talking about a network of terrorist organizations called al-Qaeda, that happens to be led by bin Laden, and we are talking about that network because it and it alone poses an immediate and serious threat to the United States.” To which Wolfowitz replied, “Well, there are others that do as well, at least as much. Iraqi terrorism for example.”

By early summer, Clarke was so despondent that he asked to be reassigned. “This administration,” he later testified, “didn’t either believe me that there was an urgent problem or was unprepared to act as though there were an urgent problem. And I thought, if the administration doesn’t believe its national coordinator for counterterrorism when he says there’s an urgent problem and if it’s unprepared to act as though there’s an urgent problem, then probably I should get another job.” In July, the Deputies Committee finally agreed to schedule a Principals level meeting on Clarke’s plan. But the schedule for July was already full, and in August too many Cabinet members were on vacation, so the meeting was set for September.

During that same time period, the CIA was raising alarms too. According to Kurt Eichenwald, a former New York Times reporter given access to the Daily Briefs prepared by the intelligence agencies for President Bush in the spring and summer of 2001, the CIA told the White House by May 1 that “a group presently in the United States” was planning a terrorist attack. On June 22, the Daily Brief warned that al-Qaeda strikes might be “imminent.”

But the same Defense Department officials who discounted Clarke’s warnings pushed back against the CIA’s. According to Eichenwald’s sources, “the neoconservative leaders who had recently assumed power at the Pentagon were warning the White House that the C.I.A. had been fooled; according to this theory, Bin Laden was merely pretending to be planning an attack to distract the administration from Saddam Hussein, whom the neoconservatives saw as a greater threat.”

The CIA fought back. “The U.S. is not the target of a disinformation campaign by Usama Bin Laden,” declared the Daily Brief on June 29, noting that the al-Qaeda leader had recently told a Middle Eastern journalist to expect an attack. The following day, the CIA included in its Daily Brief an article entitled “Bin Laden Threats Are Real.” On July 1, the Brief predicted that an attack “will occur soon.”

Then, on July 10, Tenet and CIA counterterrorism head Cofer Black held an emergency meeting with Rice to push for action against Bin Laden. But according to Woodward’s State of Denial, “both felt they were not getting through to Rice.” She “seemed focused on other administration priorities, especially the ballistic defense missile system that Bush had campaigned on” and “Tenet left the meeting feeling frustrated.”

By this point, staffers at CIA counterterrorism headquarters had grown so dejected that they, like Clarke, debated asking for a transfer.

The warnings continued. On July 11, the CIA sent word to the White House that a Chechen with links to al-Qaeda had warned that something big was coming. On July 24, the Daily Brief said the expected al-Qaeda attack had been postponed but was still being planned. Finally, on August 6, the CIA titled its Daily Brief: “Bin Ladin Determined to Strike the US.” The briefing didn’t mention a specific date or target, but it did mention the possibility of attack in New York and mentioned that the terrorists might hijack airplanes. In Angler, Barton Gellman notes that it was the 36th time the CIA had raised al-Qaeda with President Bush since he took office.

On September 4, the Cabinet met and despite Defense Secretary Donald Rumsfeld’s insistence that Iraq represented the greater terrorism threat, it approved Clarke’s plan to fight al-Qaeda. On September 9, the Senate Armed Services Committee recommended taking $600 million from the proposed missile defense budget and devoting it to counter-terrorism. According to Gellman, Rumsfeld recommended that Bush veto such a move.

On the morning of September 11, 2001, Clarke’s anti-al-Qaeda plan was sitting on Bush’s desk, awaiting his signature. It was the ninth National Security Presidential Directive of his presidency.

Would the Bush administration have stopped the 9/11 attacks had it taken the threat more seriously? Possibly. On August 3, a Saudi named Mohamed al-Kahtani tried to enter the United States in Orlando, Florida, allegedly to participate in the 9/11 plot. He was sent back home by a customs official whose only concern was that he might become an illegal immigrant. On August 16, FBI and INS agents in Minnesota arrested another potential hijacker, Zacarias Moussaoui, after being tipped off by his flight instructor. But despite numerous requests, they were denied permission to search his apartment or laptop. These incidents “might have exposed the” 9/11 plot, writes Eichenwald, “had the government been on high alert.”

Clarke makes the same argument. When the Clinton administration received word of a potential attack in December 1999, he notes, President Clinton ordered his national-security adviser to “hold daily meetings with the attorney-general, the CIA, FBI.” As a result, the leaders of those agencies instructed their “field offices to find out everything they can find. It becomes the number one priority of those agencies.” This vigilance, Clarke suggests, contributed to the arrest on December 14 of an Algerian named Ahmed Ressam, who was arriving from Canada with the aim of detonating a bomb at Los Angeles International Airport.

The Bush administration could have done similar in 2001. “Buried in the FBI and CIA,” Clarke notes, “there was information about two of these al-Qaida terrorists who turned out to be hijackers [Khalid al-Mihdhar and Nawaf al-Hazmi]. The leadership of the FBI didn’t know that, but if the leadership had to report on a daily basis ... to the White House, he would have shaken the trees and he would have found out those two guys were there.”

Would that have foiled the 9/11 attacks? “There was a chance,” Clarke argues, but top Bush officials “didn’t take it.”

When Donald Trump hurls insults at his opponents, respectable people generally roll their eyes. But it is precisely Trump’s refusal to be respectable that helps him spark debates that elites would rather avoid. And sometimes, those debates are important to have.

Given that George W. Bush’s advisers still dominate the Republican foreign-policy establishment—an establishment that has not broken with his ideological legacy in any fundamental way—his record both before and after 9/11 remains relevant to the terrorism debate today. For many years now, that foreign-policy establishment has insisted that questioning Bush’s failure to stop the September 11 attacks constitutes an outrageous slur. That’s why Fleischer is now calling Trump a “truther.” He’s purposely blurring the line between accusing Bush of having orchestrated the attacks and accusing Bush of having been insufficiently vigilant in trying to stop them. But Bush was insufficiently vigilant. The evidence is overwhelming.

If Jeb’s loyalty to his brother makes it impossible for him to confront that, fine. But he has no right to demand that the rest of the public avert its eyes.