Ten years ago today, George Tiller, a Kansas abortion doctor, was attending Sunday service at his Wichita church when he was fatally shot by an anti-abortion extremist.

"However profound our differences as Americans over difficult issues such as abortion, they cannot be resolved by heinous acts of violence," President Barack Obama said in a statement after his death.

Since Roe v. Wade made abortion legal in 1973, anti-abortion groups and individuals have targeted reproductive health care facilities and their staff with tactics ranging from protests to arson to violent attacks. An analysis in the American Journal of Obstetrics & Gynecology from 1991 said after Roe, anti-abortion violence was an "epidemic," citing 110 cases of bombing or arson in roughly 10 years.

In the last few decades, violence has continued:

In 1998, survivalist Eric Rudolph bombed clinics in Alabama and Atlanta, killing two people.

In 2013, Benjamin David Curell entered a Bloomington, Ind., clinic armed with a hatchet and vandalized the offices with red paint.

In 2015, Robert Lewis Dear entered the Planned Parenthood of the Rocky Mountains clinic in Colorado Springs armed with an assault-style rifle and killed three people.

As a number of laws restricting abortion sweep across the South, reproductive health care advocates are concerned in the current political climate, violence could escalate.

Since 1977, 11 people have been murdered as a result of attacks on abortion clinics or doctors, according to the National Abortion Federation, which has compiled statistics on such incidents of "violence and disruption" for decades. In its 2018 annual report, the group found that while death threats and threats of harm decreased slightly from the previous year, there was an escalation in vandalism, trespassing, hate mail/harassing phone calls, Internet harassment, picketing and obstruction.

"Death threats are down this year but the implied threats ... are their own form of violence," said Katherine Ragsdale, the National Abortion Federation's interim president and CEO. "They are implicit death threats even if no one says, 'I'm going to kill you.' I was recently visiting with one of our clinic's extraordinary doctors who has a young family. People are outside her work, outside her home, holding poster-sized pictures of her declaring her a 'murderer.' The signs don't say 'I'm going to kill,' so it doesn't hit our statistics as a death threat, but they are certainly incitements to violence."

The National Right To Life Committee (NRLC), one of the nation's largest pro-life organizations, said it explicitly condemns violence against abortion providers.

"NRLC strongly opposes any use of violence as a means of stopping the violence that has killed more than 60 million unborn children since 1973," the group said in a statement to USA TODAY. "NRLC has long had a policy of forbidding violence (or illegal activity) by its staff, directors, officers, affiliated state organizations and chapters. NRLC’s sole purpose is to protect human life."

Ragsdale says her organization takes all threats of violence seriously. The National Abortion Federation provides security consultation and training to clinics and their staff.

Lauren Rankin volunteers as an "escort" at an abortion clinic in Englewood, New Jersey, helping women enter the clinic safely and often acting as a barrier between patients and protesters. Rankin says in the last few years, she's seen protesters grow more "hostile."

"You always heard things like, 'you're a murderer, don't kill your baby,'" she said. "If a woman's boyfriend or husband is with her, you may hear someone say, 'don't let her murder her baby.' But in the last couple of years the rhetoric has turned more political: 'We're coming for you, we're coming for Planned Parenthood ...' It's a different level of hostility and aggression."

Republicans have amped up their anti-abortion rhetoric. Speakers at the Conservative Political Action Conference in March accused Democrats of supporting “infanticide. Trump said Democrats support "executing babies." In an event in Wisconsin in April, he falsely characterized late term abortions.

"The baby is born," Trump said. "The mother meets with the doctor. They take care of the baby, they wrap the baby beautifully. And then the doctor and the mother determine whether or not they will execute the baby."

Politifact called the claim false and "a distortion."

Advocates are concerned this rhetoric can be used to incite violence. The National Abortion Federation said Dear's attack in Colorado was connected to the release of heavily "misleading" videos which portrayed doctors as "evil," "vile," and "inhumane."

"I've been in this movement 35 years, I've watched the rollercoaster. What's different and heightened in 2019 is that the demonizing, dehumanizing, deliberately violent, misleading rhetoric used to come from extremists, and now you're hearing it at the State of the Union, from the president, from Congress and state legislatures," Ragsdale said. "It's become normalized. I anticipate it will continue to incite the violent folks among us to become more violent. When you hear that rhetoric coming from so-called 'legitimate,' sources, it emboldens the extremists and they test waters to see what they can get away with. It creates a tornado cycle feeding on itself, feeding on itself, feeding on itself, and people end up dead."

Ragsdale said it's important to make clear that threats of violence are directed toward abortion providers and staff, not toward pregnant women.

"The worst part is getting through the picketers. We don't want to scare people from getting the healthcare they need," she said. "We also don't want to encourage counter-protesters. All that does is put more people out there and women don't know who is there to support them and who is there to threaten them. People who want to show their support should contact their clinic directly."

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