CAMBRIDGE – In the summer of 2015, former Canadian Prime Minister Stephen Harper looked set to win his fourth consecutive election, scheduled for that October. Instead, his Conservative Party won just 99 of the House of Commons’ 338 seats. The party did not win a single constituency in Toronto or the entire Atlantic seaboard. Instead, the Liberal Party, led by Justin Trudeau, ended up obtaining the second-largest parliamentary majority in its history – 184 seats – despite having started the electoral campaign in third place.

That rapid reversal of fortunes was triggered by events thousands of miles away. In the early hours of September 2, 2015, in Bodrum, Turkey, a Syrian Kurdish family boarded a dinghy to try to reach Greece. A few minutes later, the dinghy capsized, and Rihanna Kurdi, together with her two children, Ghalib and Aylan, drowned. A Turkish photographer, Nilüfer Demir, posted on Twitter an image of three-year-old Aylan Kurdi’s body lying on the beach. The picture shocked the world – and ended Harper’s political career.

The previous spring, Harper had ordered Citizenship and Immigration Minister Chris Alexander to review Canada’s refugee policy, in order to ensure that terrorists were not being admitted – a move that brought the system almost to a halt. A month earlier, he had considered prohibiting the use of the niqab in public services, raising suspicion about the true motive behind the decision on refugees.

Aylan Kurdi’s aunt – Tima Kurdi, a resident of Vancouver – had been trying to get him and his family into Canada, but Harper’s refugee decisions had prevented it. Suddenly, a policy purportedly intended to protect Canadians from Islamist terrorism became a policy that offended Canadians’ sense of who they were: an open, compassionate society. Harper paid dearly for it.

Things could not be more different south of the border. There, Donald Trump won last November’s presidential election, having promised voters a travel ban on Muslims, a wall on the Mexican border, and a "deportation force.” Trump’s first attempt to implement his travel ban was struck down by the courts, but only after creating havoc at airports, confusion within universities, and disruption of families. And now the Trump administration is preparing a new travel ban.

Two possible reasons, based on recent advances in psychology and neuroscience, may explain why Americans and Canadians are reacting so differently. The first is based on insights into decision-making under uncertainty offered by so-called prospect theory, developed in the 1980s and 1990s by Daniel Kahneman and Amos Tversky.

Any immigration restriction, Kahneman and Tversky would say, implies a trade-off between two errors. A Type I error involves admitting a potential terrorist. A Type II error involves stopping innocent foreigners. To formulate an appropriate policy requires balancing these two risks, given their relative likelihoods and how much you care about the saved lives of residents and the disrupted lives of potential immigrants. How many innocent lives are you willing to disrupt or endanger to avoid a terrorist attack?

Kahneman and Tversky argued that when calculating probabilities, people make systematic mistakes. They do this by searching their memory for examples. If they are reminded of the attacks in Paris and Nice, they will overestimate the probability of terror. If they are exposed to the photograph of Aylan Kurdi, they might think otherwise.

By manipulating the salience of a memory, you affect the perception of risk and the calculus of the decision. This may be why the Trump camp has been exaggerating the risks of terrorist attacks by inventing new ones, such as the "Bowling Green Massacre” and, more recently, an unspecified non-event "last night in Sweden.”

Trump may argue that any risk to an American is unacceptable, regardless of how many Aylan Kurdis die and how many lives are disrupted. But, in that case, how can he ask US soldiers to put their lives in danger in Mosul or Kandahar? Is the demand for such a sacrifice not justified – at least in part – by a concern for the wellbeing of others? Is it really an American tradition not to care about what happens to others?

The second insight from psychological research, summarized by Bruce Hood in his recent book The Self Illusion, relates to the role of consciousness in decision-making. Recent laboratory research shows that our conscious thoughts devise, ex post, compelling rationales for many decisions that our brains tend to make unconsciously.

For example, former US President George W. Bush might have decided to invade Iraq and topple Saddam Hussein for many reasons: strategic advantage, humanitarian concern, and even competition with his father. Most of them did not involve weapons of mass destruction. But the WMD argument was used, because it was the most easily justifiable, given the context.

Is the travel ban really about protecting Americans, or might there be other motives? Consider the fact that the travel ban was applied to seven countries. Why is country of origin viewed as a useful predictor of who is likely to be a terrorist? After all, no Muslim refugee has ever committed a terrorist act in the US, and no terrorist acts have been committed in the US by nationals of the seven countries Trump has targeted.

Is a Syrian cancer patient or a distinguished Iranian academic any riskier just because of his or her country of origin? Can we not trust the State Department and the intelligence services to make these judgments, without exclusive recourse to the information on country of origin?

The point is that a travel ban on Muslims – or the Mexican border wall, for that matter – may be less related to their expressed justifications than to other, even unconscious considerations. After all, the policy was designed not by the domestic security establishment, but by Trump’s chief strategist, the avowed culture warrior Stephen Bannon.

People may well support such measures because they worry that if people who are not really like "us” are allowed to become part of "us,” we will no longer really be "us” anymore. But would we really be "us” if we renounced our openness and compassion?

Ricardo Hausmann is Director of the Center for International Development at Harvard University and a professor of economics at the Harvard Kennedy School.

Copyright: Project Syndicate.