Everything I write is written as a reasonably informed layman, not a researcher or expert in psychology or sociology or political science or any other science. I have not searched the web to see if my thoughts presented here have already been expressed by researchers with recent data.
The Great Course that I am currently listening to is How You Decide, about the science of decision-making. One of the points that particularly caught my attention is the importance of the two-system model of the human brain and mind. System 1 is the non-conscious, habitual, emotional, fast, parallel-processing older part of the brain/mind, and System 2 is the conscious, slow, one-track processing part. Automatic knee-jerk reactions come from System 1, and in any decision-making situation where System 2 isn't paying attention, those reactions become decisions. When System 2 is paying attention to the output of System 1, the System 1 output may be approved, modified or rejected. For MOST people, MOST of the time, MOST System 1 output is not monitored or modified by System 2. It is literally more mental effort to consciously evaluate a rational argument than to make an emotional response. System 2 is also more subject to fatigue or overloading, so a person dealing with a lot of stress or other demands for conscious attention is even more likely to make unmonitored System 1 decisions.
Apply that insight to American politics, and you see a distinction between the best qualities for an office-holder and the qualities likely to win elections. A good office-holder should be rational and fact-driven, with control of their emotions, but a candidate who triggers emotional responses from the voting population is more likely to get in office.
Regarding emotions, the kind of emotions also matter. The approacher / avoider distinction and more nuanced refinements of it are made because some people are motivated more by desires/goals and some more by fears, and most people weigh avoiding negatives more strongly than seeking positives. Unfortunately, negative campaigning often works because of these imbalances.
Add to that the massive cultural divide between people who trust different sources of information, and you see more. My view of media is that more liberal media tend to be better at reporting facts and that right-wing media do a lot more slanting and distorting and outright lying, but that is MY bias as a member of the science-trusting subculture. People in the science-denying subculture generally trust the media I distrust and vice versa.
The cultural split is reinforced by another aspect of human nature. We tend to select and accept new input that is congruent or consistent with what we have previously accepted, constantly reinforcing old beliefs rather than fact-checking or otherwise challenging them. Even web search engines behave in a way that reinforces this by bringing up search results that are affected by your browsing and searching history.
Still another human weakness makes repeated lying dangerously effective. People generally don't remember the truthfulness of claims they are repeatedly exposed to, even if they checked truthfulness when exposed to the claims. Claims and their truthfulness aren't retrieved together by our memory systems, so a repeat of a lie is likely to be accepted as true because it is recognized as familiar and any knowledge that it is false is less likely to be recalled.
Given that the right-wing media have been demonizing Hillary Clinton for more than a generation, the 2016 U. S. Presidential election had a Democratic candidate working against the liability of a large segment of the population with their non-conscious habitual (System 1) minds trained to distrust her.
If we look at the last several presidential elections, we can see that TWO Democratic candidates seen as more rational than emotional (Al Gore and Hillary Clinton) have won the popular vote but not the Electoral College vote.
I suggest that if the Democratic Party wants to win the presidency, they need candidates able to appeal to voters emotionally, AND they would do better with candidates WITHOUT a lot of prior national exposure and years of national demonizing by right-wing media.
Emotion vs. reason was not the only reason for the outcome of the 2016 election. It took a lot of attacks on Hillary to keep her out of office. Here are a few of them:
Misogyny (probably).
Very unbalanced amounts of media coverage in the campaign.
Frequent repetitions of lies about her involvement in events in Benghazi, Libya.
Hammering on one bad decision about an email server.
Leaks of Democratic Party emails (hacked by Russians).
Some fraction of Bernie Sanders fans who refused to vote for Hillary.
Unprecedented meddling by the head of the FBI a few days before the election.
False comparisons that led many to assume both candidates were equally bad.
Badly misleading polls that led many people to think their votes weren't needed.
Voter/vote-suppression by the GOP.
Voter apathy.
Added later: Major Russian interference (see The Mueller Report).
At a level of gross over-simplification, I view liberals as people who control themselves and want to help other people, and right-wingers as people who help themselves and want to control other people. Unfortunately, in recent American history, that has led to increased right-wing power in office even though right-wing views are held by a DECREASING MINORITY of the American population. GOP positions on ALMOST EVERY ISSUE are out of sync with the majority of the American population, yet the GOP is in power in way too much of the country.
Beyond eliminating the Electoral College, which is unlikely to happen any time soon because the states it gives disproportionate power to will try to keep that power, some other possible reforms this country could use include:
Reform campaign finance laws.
Remove all the voter suppressing laws.
Remove all existing gerrymandering & make gerrymandering illegal.
Make voting mandatory, or at least make failure to vote cost money.
Introduce instant runoff / multiple ranked choice voting.
Increase security against foreign manipulation.