As a Republican, Mitchell Adkins complained of feeling like an outcast at Transylvania University in Lexington, Ky. “Hardcore liberals” made fun of him, he wrote, and he faced “discrimination on a daily basis.” He soon dropped out and enrolled in trade school.

But his simmering rage led him back to campus one morning in April 2017, when Adkins pulled out a machete in the campus coffee shop, demanded that patrons state their political affiliation and began slashing at Democrats.

“There was never any ambiguity about why he did it,” said Tristan Reynolds, 22, a witness to the attack, which left two women injured.

Over the past decade, attackers motivated by right-wing political ideologies have committed dozens of shootings, bombings and other acts of violence, far more than any other category of domestic extremist, according to a Washington Post analysis of data on global terrorism. While the data show a decades-long drop-off in violence by left-wing groups, violence by white supremacists and other far-right attackers has been on the rise since Barack Obama’s presidency — and has surged since President Trump took office.

This year has been especially deadly.Just last month, 13 people died in two incidents: A Kentucky gunman attempted to enter a historically black church, police say, then shot and killed two black patrons in a nearby grocery store. And an anti-Semitic loner who had expressed anger about a caravan of Central American refugees that Trump termed an “invasion” has been charged with gunning down 11 people in a Pittsburgh synagogue, the deadliest act of anti-Semitic violence in U.S. history.

This month brought two more bodies: A military veteran who had railed online against women and blacks opened fire in a Tallahassee yoga studio, killing two women and wounding five. All told, researchers say at least 20 people have died this year in suspected right-wing attacks.

While Trump has blasted Democrats as “an angry left-wing mob” and the “party of crime,” researchers have identified just one fatal attack in 2018 that may have been motivated by left-wing ideologies. In February, Tierre Guthrie, an ex-Marine who was sympathetic to the far-left Black Nationalist movement, shot and killed a police officer trying to arrest him at his Georgia home for failing to appear in court for a traffic violation.

The uptick in right-wing terrorism comes amid a renewed national focus on hate-driven violence. The Anti-Defamation League documented a 57 percent surge in anti-Semitic incidents in 2017, especially at schools and on college campuses. Meanwhile, FBI statistics released this monthshow reported hate crimes jumped 17 percent last year.

Among them was the vehicle attack in August 2017 that killed one person and injured 35 others protesting a rally by white supremacists in Charlottesville. The accused driver, James Alex Fields Jr., 21, faces up to life in prison for multiple charges in a trial set to begin Monday.

Terrorism researchers say right-wing violence sprouted alongside white anxiety about Obama’s presidency and has accelerated in the Trump era. Trump and his aides have continuously denied that he has contributed to the rise in violence. But experts say right-wing extremists perceive the president as offering them tacit support for their cause.

After the violence in Charlottesville, for example, Trump asserted that “both sides” were equally to blame and that there were “some very fine people” among the far-right demonstrators, many of whom wore “Make America Great Again” caps while chanting racist and anti-Semitic slogans.

More recently, Trump rallied crowds in the run-up to the Nov. 6 midterm elections with incendiary rhetoric about Muslims and immigrants, terming a caravan of Central American refugees an “invasion” and ordering active-duty troops to the U.S.-Mexico border.

“If you have politicians saying things like our nation is under attack, that there are these marauding bands of immigrants coming into the country, that plays into this right-wing narrative. They begin to think it’s okay to use violence,” said Gary LaFree, criminology chairman at the University of Maryland and founding director of the National Consortium for the Study of Terrorism and Responses to Terrorism, or START.

Frank Figliuzzi, a former FBI assistant director for counterintelligence, said political leaders, “from the White House down, used to serve as a check on conduct and speech that was abhorrent to most people. I see that eroding.”

“The current political rhetoric is at least enabling, and certainly not discouraging, violence,” Figliuzzi said.

START maintains the federally funded Global Terrorism Database, the most comprehensive list of terrorist attacks available to the public. The database tracks terroristic incidents in the United States and around the world since 1970, defined as the threatened or actual use of violence by nonstate actors seeking to attain political, economic, religious or social goals through fear or intimidation.

Determining motivation is an imperfect science, and many acts of domestic terrorism do not sort neatly along the ideological spectrum. In many cases, such as last year’s shooting at a Las Vegas music festival that left 58 people dead, the motive is unknown.

On Oct. 1, a crowd of thousands had gathered in Las Vegas for a music festival. Then bullets rained down from the sky. Survivors describe the shock and terror of the worst mass shooting in recent U.S. history. (Video: The Washington Post)

Where motive can be identified, researchers have divided the incidents into about a dozen categories, such as “jihadi-inspired extremists,” “anti-LGBT extremists” and “anti-government extremists.” For recent cases, The Post sorted those categories according to ideology, then refined the data through a case-by-case review.

The results show that unlike the turbulent 1970s, when environmental, antiwar and other left-wing groups were responsible for historically high rates of terrorism in the United States, today’s attackers are far more likely to have right-wing sympathies.

Of 263 incidents of domestic terrorism between 2010 and the end of 2017, a third — 92 — were committed by right-wing attackers, according to The Post’s analysis. Another third were committed by attackers whose motives were either unknown or not clearly political.

Islamist terrorists committed 38 attacks. And left-wing attackers were responsible for 34 attacks — about 13 percent.

Among the most deadly left-wing attacks were the 2016 killings of eight police officers in Dallas and Baton Rouge by gunmen sympathetic to the Black Lives Matter movement. One of the most prominent was last year’s attack on Republican members of a congressional baseball team, including House Majority Whip Steve Scalise (La.). The gunman, James Hodgkinson, had raged against Trump online and was a supporter of Sen. Bernie Sanders (I-Vt.).

Majority Whip Steve Scalise (R-La.) and others were wounded on the morning of June 14 when a gunman, identified by law enforcement as James T. Hodgkinson III, opened fire on a congressional baseball practice in Alexandria, Va. (Video: Monica Akhtar/The Washington Post)

Joshua D. Freilich, a criminologist at John Jay College and co-director of the Extremist Crime Database, an open-source database of violent and financial crimes committed by political extremists, said that right-wing attacks not only happen more often but also are more likely to result in fatalities than left-wing attacks.

Stacey Hervey, a criminologist at the Metropolitan State University of Denver who has studied radicalization, said the attackers generally fit one of three archetypes: thrill-seekers, such as teenagers who paint swastikas on the sides of buildings; reactive attackers, who lash out suddenly at perceived enemies; and mission-oriented attackers, who aim to send a specific message or achieve a certain political goal.

Adkins, who pleaded guilty this month to the machete attack in Transylvania University’s Jazzmans Cafe, falls into the reactive category.

In a 2015 letter to the student newspaper, Adkins wrote that “being a Republican in this school makes me such a minority that I’ve had to face discrimination on a daily basis.” Online, he later complained about “hardcore liberals” and announced that he had dropped out of college because “the constant bullying and lack of friends drove me to an overdose, a trip to the hospital and two trips to the mental hospital.”

Prosecutors and Adkins’s attorney declined to comment on the case. Adkins’s mother, Amy, said her son is filled with “remorse and sorrow.” She believes that he was driven less by his conservative views than by feelings of marginalization and disrespect.

“It’s not a question of being right-wing,” she said. “It’s a question of feeling that you’re required to give credence to what people believe, but they aren’t required to give you the same respect, regardless of what the issue is.”

As a result of the attack, Transylvania President Seamus Carey said the 1,100-student campus has adopted civility as its theme this year. But Carey said it can be hard for students to be civil when society has grown so coarse.

When political and religious institutions “lose their moral authority,” Carey said, “all the people who relied on that can feel a little lost.”

Even more menacing, Hervey said, are the mission-oriented attacks. The Pittsburgh synagogue shooting was the deadliest act of anti-Semitic terror in the United States since an April 2014 shooting rampage by Frazier Glenn Miller Jr., a former KKK member and white supremacist who has been sentenced to die for killing three people at a Jewish Community Center and a Jewish retirement home in suburban Kansas City, Kan.

Among the dead — none of them Jewish — were William Corporon, 69, and his grandson, Reat Underwood, 14.

Since losing her father and her son, Corporon’s daughter, Mindy Corporon, has focused on spreading messages of kindness. She was getting ready to board a flight from Orlando to Dallas when she got a text message about the Pittsburgh shooting.

“I was just overwhelmed with sadness. I didn’t make it to Dallas,” she said. “I’ve realized that there are people who are touched by evil.”

More recently, members of a tiny right-wing militia group came to the attention of police in connection with two acts of terror in 2017, including a pipe bomb thrown through the window of a women’s health clinic in Champaign, Ill., last November.

That bomb did not go off, but a few months earlier, one did: In August, a pipe bomb crashed through the window of the Dar Al-Farooq Islamic Center in Bloomington, Minn., and exploded a few yards from five people gathered for early morning prayers.

Police arrested members of the White Rabbit 3 Percent Illinois Patriot Freedom Fighters Militia, an anti-government group that issues its own currency and has published a handbook that calls for a return to “the good old days” and “Our Old America,” according to an investigation by Chicago’s ABC 7 Eyewitness News.

One of the group’s members, Michael McWhorter, 29, told FBI agents that the mosque bombing was not intended to kill anyone but to “scare them out of the country,” to “show them, hey, you’re not welcome here, get the f--- out,” according to court records.

No one was injured in the bombing. But Mohamed Omar, the Islamic center’s executive director, said it shattered his belief that, in America, he and his family would be safe.

“I was born in Somalia, a war-torn country, and ran 8,000 miles to get away from bombs,” Omar said. “I never thought that I would be bombed in America. My wife and my daughter kept asking, ‘Who would do this to us?’ ”

In addition to the militia members, Omar said he blames Trump and other political leaders who have demonized immigrants generally and Muslims specifically.

“When politicians speak and talk the politics of hate and division, people who don’t know us see us as an enemy,” Omar said. “These three guys came all the way from a small town in Illinois to throw a bomb at people they never met.”

Alice Crites contributed to this report.