Give John Bolton his due. By writing a book that apparently corroborates the core argument of those seeking to impeach and remove President Donald Trump, the former national security adviser has shown genuine moral courage. The literature on moral courage helps explain why: It’s because Bolton is an ideological fanatic. His fervent belief in supporting America’s allies and confronting its adversaries led him to speak up against Trump, who violated that principle by delaying aid to Ukraine in order to pressure it into investigating a political rival.

Not everyone agrees that, in speaking up now, Bolton has acted courageously. By not coming forward earlier, my Atlantic colleague Graeme Wood has argued, Bolton “waited until speaking is to his advantage” and thus procured “a huge book deal” and the ability “to command high speaking fees before rapt right-wing audiences.”

But will right-wingers really shell out large sums to hear a man who threatened the president they adore? Since the leak about his book, Bolton has been denounced by Republican Senator Jim Inhofe, who is one of his closest friends in the Senate, and Fred Fleitz, who served twice as Bolton’s chief of staff. He’s been castigated on Fox News, where he served as a contributor for 11 years. He’s put at risk his relationship with former benefactors such as the Mercer family. Surely it would have been safer to simply write a book that avoids alienating the president, as the former Trump appointees Nikki Haley and James Mattis did.

Maybe Bolton is betting that Republicans will fall back in love with him once they fall out of love with Trump. But three years into Trump’s presidency, no evidence suggests that is happening. And Bolton is too widely reviled among progressives—and too warlike—to reinvent himself as a Never Trumper with a gig as a contributor at MSNBC. So it’s hard to see how Bolton’s attack on Trump works to his advantage. Even if Bolton did time his truth telling to maximize book sales, the fact remains: He appears to have told the truth about Trump, something few prominent Republicans have had the courage to do.

To defy their bosses, friends, and allies, people need to have faith in something larger. In his 2012 book, Beautiful Souls, the author Eyal Press suggests that people who put themselves at risk to challenge injustice are often true believers who cannot bear to see the institutions they serve violate their ideals. Press tells the story of Paul Grüninger, a Swiss policeman in the late 1930s who lost his job, and became a local pariah, for violating Switzerland’s policy of denying entry to Austrian Jewish refugees. What motivated Grüninger, Press argues, was “his unshakeable conviction” in Switzerland’s self-conception as a “sanctuary whose citizens had always extended a welcome hand to castoffs from more troubled lands.” That self-conception, Press notes, was largely a myth. But because of Grüninger’s obsessive devotion to it, he risked his livelihood and reputation to prove that the legend was true.

Press also recounts the actions of Leyla Wydler, a Houston investment broker who, in 2003, mailed a packet filled with incriminating documents about her employer to the Securities and Exchange Commission. Wydler’s action, Press argues, stemmed from her unusual idealism about the American financial system, which she considered “untainted by the corruption that flourished” in her native El Salvador. Whistle-blowers, Press notes, quoting a study by Myron Peretz Glazer and Penina Migdal Glazer, “invariably … believed that they were defending the true mission of their organization”—even when the organization’s actual mission wasn’t nearly as high-minded as they believed.

Bolton fits this pattern. He believes strongly—even recklessly and obtusely—in hyper-aggressive, hyper-nationalist foreign policy. And he’ll defy anyone who deviates from that vision.

Before Trump, Bolton’s presidential patron had been George W. Bush, who endured a bitter battle with congressional Democrats for nominating Bolton to be his ambassador to the United Nations. But after leaving the job, Bolton turned on Bush for being too dovish. “Nothing can erase the ineffable sadness of an American presidency, like this one, in total intellectual collapse,” he wrote in a 2008 Wall Street Journal op-ed castigating Bush’s diplomacy with North Korea. In his 2007 memoir of his time in the Bush administration, Surrender Is Not an Option, Bolton trashed influential former colleagues for straying from his hard-line views. The criticism infuriated Bush. Key Bush advisers such as Condoleezza Rice, Robert M. Gates, and Stephen J. Hadley subsequently got their revenge by lobbying the nascent Trump administration to deny Bolton a job.

Bolton’s impolitic candor continued during the Obama years. Most hawks opposed Barack Obama’s diplomacy with Iran and urged ever harsher sanctions against Tehran. But they strenuously denied wanting war. Bolton was more honest. He wrote a 2015 New York Times op-ed titled “To Stop Iran’s Bomb, Bomb Iran,” thus making him a far easier target for liberals. In early 2018, he wrote a column advocating a preemptive strike on North Korea—which was unlikely to ingratiate himself with Trump, who had taken office promising to end America’s wars.

This isn’t to say Bolton never trims his views to suit his interests. But he does so less than government officials who are less ideologically devout. After entering the Trump administration, Bolton alienated Trump by battling ferociously against the president’s penchant for big, headline-grabbing deals with adversaries such as North Korea and the Taliban. Rivals within the government accused Bolton of disloyalty for allegedly refusing to go on television to defend administration policies he opposed. When Bolton left, Trump replaced him with the sycophantic Robert O’Brien, who has called the president “the greatest hostage negotiator that I know of in the history of the United States.”

Bolton’s departure is probably healthy for world peace. His ideological zeal—which led him to continue to defend the wisdom of invading Iraq long after many others had admitted their mistake, and to propose new wars in North Korea and Iran—made him one of the most dangerous national security advisers in American history. But that very obstinacy—Bolton’s unyielding devotion to an ultra-hawkish foreign policy—may be the same quality that has now led him to challenge the GOP impeachment narrative. Bolton appears to loathe Vladimir Putin. And he’s incapable of whitewashing America’s betrayal of Ukraine, an ally under Russian threat. Dov Zakheim, a former undersecretary of defense who has known Bolton for decades, told me that Bolton would “take on the world if necessary, as long as he believes in what he believes in.” Luckily for the republic, taking on the world includes taking on Donald Trump.