Khulud Fidama, 26, of Dearborn, Mich., stands with her family on Jan. 29 outside the McNamara Terminal at Detroit Metropolitan Airport to protest President Trump's travel ban for refugees and citizens of seven Muslim-majority nations. (Elaine Cromie/Detroit Free Press via AP)

With the stroke of a pen, President Trump signed into law this week a series of executive orders that have sent reverberations around the world. Making good on some of his most controversial campaign promises, Trump started on Wednesday the process of building a wall between the U.S. and Mexico. On Friday, he instituted a ban on refugees and halted admission to all foreign nationals — including those with visas — of seven Muslim-majority countries, including Syria, Iraq and Iran.

By early Saturday, refugees were being detained at the border, and some legal permanent residents were turned away. In short order, massive crowds demanding that the policy be revoked rallied at the airports of many of the nation’s largest cities, including New York, Los Angeles, Chicago and Boston.

It is clear that Trump’s policies reflect a sea change in the American approach to national security — but do they “make Americans safe again?”

Our research suggests they could do exactly the opposite. By dehumanizing minority group members in word and deed, Trump’s rhetoric and policies may promote the very actions that they purport to prevent.

During the presidential primary process, we collected data from two large samples of several-hundred Americans online. We assessed their political leanings, their attitudes about Mexican immigrants and Muslims, and their support for several of Trump’s actual border policies (taken directly from his campaign website).

Specifically, we assessed participants’ overt dehumanization of Mexican immigrants and Muslims, first by asking Americans to place these groups where they thought they belonged on the popular “Ascent of Man” diagram representing human evolution, and second by asking how well they thought Mexican immigrants and Muslims were characterized by animalistic traits such as being “savage,” “primitive,” “lacking in self-control” and “unsophisticated.”

Our work, published last month in Personality and Social Psychology Bulletin, revealed that Americans consistently rated Mexican immigrants and Muslims as less human than average Americans. Furthermore, reported levels of dehumanization strongly predicted support for Trump’s immigration policies, including the plan to build a wall between the U.S. and Mexico and the proposal to ban Muslim immigration to the U.S.

Suggesting the unique importance of dehumanization, these associations remained when we controlled for participants’ political conservatism and their dislike of Mexican immigrants and Muslims. We also observed that support for Trump as a candidate was more strongly linked to dehumanization of these groups than support for any of the other Republican candidates. It wasn’t even close.

Our work also suggests that the consequences of dehumanization do not stop with the policies it promotes. There are consequences, too, to making others feel dehumanized.

To examine the ramifications of dehumanization for its targets, we sampled Latino and Muslim residents of the U.S. online and asked them to report how dehumanized they felt by Donald Trump, the Republican Party, and Americans in general. Our findings revealed that our samples of Latinos and Muslims felt heavily dehumanized, and that this had important consequences: The more dehumanized they felt, the more likely they were to support violent over nonviolent forms of collective protest, and the less likely they were to report suspicious activity in their neighborhoods, potentially related to terrorism, to the FBI. Here again, these associations remained even after controlling for feelings of being disliked and for participants’ levels of political conservatism.

These findings highlight the self-reinforcing dangers dehumanization can create. When one group dehumanizes and aggresses against another, those on the receiving end may come to feel dehumanized and reciprocate the hostility. This could then be interpreted by the first group as further evidence of their lack of humanity. Highlighting the potential for such processes to provoke reciprocal cycles of hostility, Iran responded Sunday to Trump’s immigration ban by announcing that there would be “proportionate legal, consular and political consequences.”

By insinuating that Muslims and Mexicans are less “evolved” than “us,” and by putting forward blanket measures to keep “them” out at all costs, Trump risks framing Mexican immigrants and Muslims not as human peers to be reasoned with, but as an undifferentiated, threatening mass to be neutralized.

Reflecting on Trump’s proposals a few months ago, then-President Barack Obama remarked, “That’s not the America we want. It doesn’t reflect our democratic ideals.” Although the election results reveal important disagreements about what people want America to be, there is broad agreement across the political divide about the desire to keep Americans secure. For that reason alone, everyone should be troubled that our findings lend empirical backing to the rest of Obama’s statement: “It will make us less safe.”

Nour Kteily is assistant professor of management and organizations at the Kellogg School of Management at Northwestern University.

Emile Bruneau is research associate at the Annenberg School for Communication at University of Pennsylvania.