Michelle Obama, Barack Obama, Hillary Clinton, Chelsea Clinton, and Bill Clinton greet supporters during a campaign rally on Independence Mall on November 7th, 2016, in Philadelphia, Pennsylvania. (Photo: Justin Sullivan/Getty Images)

Inclusiveness is a core value of the Democratic Party. "We're all on the same team," President Barack Obama declared the day after Donald Trump was elected to succeed him. "We're all Americans."

Republicans, driven by a value system that emphasizes group loyalty, are far less likely to share those sentiments. And according to new research, their us-vs.-them attitude may have helped them win the 2016 election.

"The Democrats' greater inclusiveness meant that they struggled to view Hillary Clinton as representative of the group," University of Birmingham psychologist Julie Christian, lead author of the study, said in announcing the findings. The more homogenous Republicans, in contrast, clearly saw Trump as their guy, which gave them more incentive to get out and vote.

In the journal Leadership, Christian and her colleagues examine the 2016 election through the lens of group dynamics. Drawing on Jonathan Haidt's "moral foundations" structure, which argues liberals value fairness and prevention of harm, while conservatives emphasize loyalty and respect for authority, they tested whether the Democrats' all-embracing attitude put them at a disadvantage.

The study featured 229 Americans recruited online in the week before the 2016 election—half of them Democrats, half Republicans. Using a one-to-five scale, they were asked how similar their views were to fellow party members, and to supporters of the other party.

They were also asked the degree to which they felt their party's candidate (Clinton or Trump) embodied their group's norms. Then, using a one-to-100 scale, they indicated how strongly they supported their party’s candidate.

The researchers report Democrats were far more likely to assert their views and values were similar to those of Republicans than vice-versa. This reflects the fact that liberal values "facilitate a sense of similarity and inclusion."

"Their flexibility directly works against the group's cohesiveness, and hampers the chance of a win," the researchers write.

In contrast, Republicans made a "clear distinction" between the parties, and they identify more strongly as a member of the party. This group identity "acts as a 'glue' for the membership," creating a more cohesive and unified party.

In line with this, "Trump was viewed as a more prototypical leader by Republican than Clinton was by Democrats," and thus more worthy of support. "These results may help to explain the perhaps surprising fragility of Democrat voters' support for Clinton," the researchers conclude.

Christian and her colleagues are quick to note that, while an us-vs.-them mindset may win elections, it can make governing more difficult. When it comes to actually running the country, "the inclusiveness approach of the Democrats would likely work to pull the competing parties together," they write.

But during the campaign, they add, that attitude led to "a loss of momentum" for the party, and "likely contributed to the Democrats' loss."

Is this a problem for Democrats moving forward? Very possibly. Democrats take pride in emphasizing the common bonds we all share—a lovely thought that may come at an electoral price.

The results suggest the party needs to articulate a binding philosophy that clearly differentiates Democrats from Republicans, and find a leader who unambiguously personifies it.