Illustration by Jim Cooke

History regularly offers up events that turn out to be litmus tests for political courage, wisdom, and judgment. The last one was the Iraq War. The new one is the candidacy of Donald Trump.

Think back, if you will, to the immediate post-9/11 era. Passions were high. The public was fearful and filled with an overriding directionless anger. A cabal of powerful political figures with few scruples seized this opportunity to launch a war of choice against Iraq, driven by ideology and papered over with a thin veneer of lies and propaganda. Their tactics were not particularly hard to spot. But they were able to tap into the public’s fear and anger to generate a powerful wave of popular support for their plan. And because of that, all of the people who were in positions to stop the tragic mistake from proceeding fell into line. The House and the Senate fell into line. Political pundits fell into line. The entire government fell into line. Even though the Iraq War was a folly—and even that folly could be seen clearly before it happened—falling into line was the easier path. It offered less friction. It required no courage, or foresight. It was an act of going along with the crowd for the sake of political expediency. And most of our leading lights went along like good little soldiers.

We now know that the Iraq War was one of the worst decisions in the history of the United States. It caused the death of hundreds of thousands of people; it destabilized an entire region of the world; and it wasted a pile of money that could have accomplished amazing things back home. It is now uncontroversial, even among Republicans, to acknowledge that the Iraq War was Not Good. And with the passage of time, the scope of its folly will become even more clear. When the history books are written, those who fell in line to support the Iraq War for the sake of political expediency will be remembered as cowards who failed their biggest moral test.

These sorts of political issues that act as tests of a generation of political leaders happen every so often. When we look back at the leaders of the 1960s, we ask: Did they support civil rights? Or did they snivel and shrink and acquiesce to the institutional racism that was politically popular at the time. When we look back 100 years earlier, we ask: Did they speak out against slavery? Or did they shrug and go on with other business for the sake of their careers? Many public figures who might have been able to slip quietly into the history books as solid, upright model citizens find themselves exposed as moral weaklings by the defining issue of their own era.

Standing up against an overwhelming tide of wrongness is not easy. It goes against the fundamental political instinct of self-preservation. It is an indicator of moral courage—a quality which does not perfectly overlap with the qualities necessary to become an American public figure. In the long run, though, those who fail these tests corrupt their own legacy, and often never get the chance to work themselves back onto the right side of history.

Which brings us to Donald Trump. At first, no one took him seriously. Then, when it became clear that he was a force to be reckoned with, the political establishment reacted with revulsion. The left reviles him for his racism, and know-nothing denial of reality; the right reviles him in large part because they find him to be insufficiently conservative and a distasteful, crude face of the Republican Party. As we draw closer to the nomination process, though, we also draw closer to the period when political pressure to fall in line and support Donald Trump’s candidacy will start to become very strong, for Republicans. If Trump wins the nomination, the very Republicans who have been denigrating him for months will be faced with the prospect of becoming good soldiers in the Trump Army, or else acknowledging the unthinkable: another four years of a centrist, hawkish, business-friendly Democrat. Already, members in good standing of the Republic Establishment are preparing their Trump endorsements. Their ranks will only grow.

This week, scientists intensified their warnings about climate change, saying that without drastic action we could face storms of unprecedented severity and the flooding of coastal cities around the world in a matter of decades. Also this week, Donald Trump said, “I am not a great believer in man-made climate change.” His response to a single terrorist attack on a different continent is to advocate open torture and closed borders. Three months ago, Donald Trump proposed barring all Muslims from coming to America—the single most astoundingly xenophobic and backwards policy proposal from a serious candidate in years. (Trump’s opponents are only now beginning to match his appetite for outrageous Islamophobia.) There need be no further discussion of his candidacy, after that. That cannot be condoned. That cannot be bargained away. That is a wrong so heavy that nothing on the other side of the scale will balance it out. We can set aside all of the funny, clownish aspects of Donald Trump and focus only on his serious policies; those alone are plainly immoral and racist. Combined with his narcissism, thin-skinned personality, routine lying, and tendency to lash out blindly at all detractors, and he is not funny at all. He is dangerous. And no one who decides to support him for political reasons can later claim that they did not know he was dangerous.

Donald Trump has a base of supporters. But that base is not enough for him to win. For him to win, he must gain the support of a large number of Republicans who consider themselves to be responsible, moral adults. The political pressure to support Trump is only beginning. The popular tide behind him may well grow. This is the time when making the choice that is clearly wrong may start to look appealing. It may soon appear to be the path of least resistance.

If you make the cowardly choice, history will not forget.