Exactly 20 years ago, as the Boston Globe’s New York bureau chief, I interviewed Mayor Rudy Giuliani in his office in City Hall. The 1996 Republican Convention was going on in San Diego, and I asked him why he wasn’t there. “It’s not my sort of thing,” he replied. “I’m much closer to moderates in both parties than to extremists in either.”

That was a long time ago.

Four years later, he was preparing to run against Hillary Clinton in what many foresaw as the most exciting Senate contest of 2000. But he dropped out before the race got under way, reeling from a cancer diagnosis, a divorce, and the realization that his heart wasn’t in it. He skipped a major fundraising lunch in Albany to attend a Yankees game (a move that spoke well of him). When he withdrew, he said of Clinton, “She’s a nice lady.”

That too was a long time ago.

A year later came the Sept. 11 attacks, and Giuliani stood firm, read Churchill’s memoir of the London blitz, and performed admirably as the spirit of a brave city. Then, gradually, he started believing his own hype, started giving speeches not just on urban affairs and crime-fighting (for which he had demonstrable expertise) but also global terrorism (about which he knew little). He started insinuating himself into the Republican Party. He made a disastrous run for president in 2008, ending up with one delegate after spending $50 million. Some said that he was too liberal for the Republican Party. (He advocated gun control, gay rights, abortion rights, and immigration reform, as do most New York mayors by nature.) He may have come to the same conclusion. He turned to the right.

And that brings us to his speech Monday, on the first night of the 2016 Republican National Convention, a speech that would have made the mayor of 20 years ago roll his eyes and giggle. Self-righteous and bombastic as he has become in recent years, I have never seen him—I have never imagined him—huffing and puffing with such fire and brimstone. Or spewing such rank nonsense.

Boasting that he changed New York “from the crime capital of America to the safest large city in America,” he said, “What I did for New York, Donald Trump will do for America.” Stipulating that he played a role in cutting crime in New York (and I think he did, to some extent), what did he do? Most pertinent, he appointed William Bratton as his police chief, who tracked crime with daily computer statistics (before then, there were only quarterly statistics), then instantly redeployed cops to neighborhoods where crime was spurting. He also arrested people for committing small crimes, and many of those people, it turned out, were wanted for large crimes. Other things were happening in society, too. But these techniques and the surrounding circumstances have no application to the fight against global terrorism. Nor does the sophisticated approach that Giuliani and Bratton brought to urban disorder have any resemblance to Trump’s attitude to anything.

Then Giuliani delved into the shallowest realm of Trump’s attack on Obama’s (or Obama-Clinton’s) counterterrorism policies—the refusal to call our enemy by their name: as he bellowed it, “Islamic extremist terrorism” (words that drew an enormous ovation). Obama has addressed this critique: It is silly to believe that, if only he uttered those three words (like “Beetlejuice, Beetlejuice, Beetlejuice!”), the bad guys would turn and run—or anything different would happen whatsoever. “If they are at war against us,” Giuliani roared, “we must commit ourselves to unconditional victory against them.” What does that mean? What does the United States or the West have to do to achieve that goal? I ask Giuliani and others who speak in this language to put forth a three-point outline, a 100-page treatise—some idea of what new policies, tactics, or strategies they have in mind. I honestly don’t know, and I’m pretty sure they don’t either.

In the next sentence (right after “unconditional victory against them”), Giuliani said, “This includes undoing one of the worst deals America ever made”—the nuclear deal with Iran. Giuliani claimed that this deal “will eventually let them become a nuclear power.” Meanwhile, it’s having us pour billions of dollars into a country “that is the world’s largest supporter of terrorism,” adding, “We are actually giving them the money to fund the terrorists who are killing us and our allies. Are we crazy?” (The crowd yelled, “Yes!”)

There are so many falsehoods and confusions to parse in this passage. First, the nuclear deal is holding up quite well. Iran has dismantled the centrifuges, reduced the enriched uranium, exported the heavy water, and let in the IAEA inspectors and cameras, just as the deal required. Second, the money we’re sending them—which turns out to be a lot less than they expected—is their money, which was frozen as a result of their nuclear program, with the implication that it would be unfrozen if the program was dismantled; the program has been dismantled, so the funds are unfrozen.

Third, Giuliani seems to believe—or wants to make the audience believe—that Iran is funding the terrorists who are attacking the United States and our allies, when in fact Iran (a Shiite-led country) deeply loathes ISIS and al-Qaida (a Sunni movement). In fact, after the 9/11 attacks, Iran shared intelligence on al-Qaida with U.S. diplomats. Today, Iranian-backed militias are fighting against ISIS forces in Iraq. Some U.S. officials are leery of this fact, not wanting Iran to emerge as a strategic winner in this contest, but, like it or not, in the fight against ISIS, the United States, the West, and Iran are on the same side.

If you define the enemy as “Islamic extremist terrorism,” you miss these subtleties. You think Shiite extremists, Sunni extremists, Kurdish extremists, and lone-wolf killers in the West are all the same, are driven by the same motives, and can be fought or disarmed in the same way. This is the danger of describing these conflicts in terms of such simplistic slogans. Obama’s (and Clinton’s) reluctance to recite these labels stems not from “political correctness” but from an understanding of the world’s complexities and the true nature of this fight.

“Greatness!” Giuliani screamed at the top of his lungs at the end of his speech. The crowd went wild. But if terrorists were watching, believe me (as Trump likes to say), they were not impressed.

Read more Slate coverage of the 2016 campaign.