It started when the NRA released a video that featured Dana Loesch, a conservative television host, accusing the left of using the "violence of lies" to teach children that President Donald Trump is "another Hitler," of using "their ex-president to endorse the resistance" and "their media to assassinate real news" – all of which, Loesch said, encourages people to engage in violent demonstrations. She called on viewers to join the NRA and fight back with "the clenched fist of truth."

Organizers of the Women's March, the massive Jan. 21 protest of Trumps inauguration, responded with an open letter to the NRA calling on the gun-rights group to apologize for the ad, which Women's March co-president Tamika D. Mallory called "a direct attack on people of color, progressives and anyone who exercises their First Amendment right to protest."

The NRA came back with another video castigating the "chaos creators who are trying to impose their will upon our country through violence and lies."

On July 14, Women's March has scheduled their ripost: another protest trek, this one from NRA headquarters in Fairfax, Virginia, to the Department of Justice building in Washington, D.C.

Each side has accused the other of using violent rhetoric, inciting hate and violence in the process. And the exchange has hate-watch groups and free speech advocates wondering: When is such communication dangerous, and when is it merely offensive -- but protected --speech?

"I think it's potentially dangerous, because the groundwork has been laid over the last 20 to 30 years," says terrorism expert Cynthia Storer, referring to the NRA video and other call-to-action rhetoric.

"I have friends who are libertarians who would say, 'This is all funny. This is a joke.' It's not a joke anymore, especially with all the things you hear people saying," such as calling for a revolution, adds Storer, a former CIA terrorism analyst who was part of the team that found Osama bin Laden.

"You have people stoking this. Then they start fooling themselves about what the consequences would be," she says.

Displays of highly provocative visuals and speech have become commonplace, thanks in part to easy access to social media platforms. And it's accelerated, experts say, with Trump's rise to power and penchant for provocative tweeting. During his campaign, Trump told cheering supporters that he longed for the days when protesters would be "carried out on a stretcher"; more recently he shared a doctored video showing him at a professional wrestling match, punching out a man with the CNN logo for a head. Famously blunt comedian Kathy Griffin was photographed holding a fake severed head that looked likeTrump's, covered in blood. And singer Madonna told hundreds of thousands of Women's March demonstrators in January that she had "thought an awful lot about blowing up the White House."

Griffin has apologized, Madonna said her words were taken out of context and the White House defended Trump's wrestling video as the president hitting back when attacked. But experts in rhetoric and social movements are wondering where the line lies between provoking violence and just being provocative – and what can be done when someone crosses it.

The Southern Poverty Law Center, a hate-group watchdog organization based in Montgomery, Alabama, has found that hate-related crimes and violence have increased since Trump was elected, says Heidi Beirich, who heads the SPLC's investigative project. While the evidence is one of correlation, and not provable causation, it's hard to separate the two, she says, noting that anti-Muslim attacks went up after Trump made comments demonizing the religious group.

The SPLC has long monitored the activities of the Ku Klux Klan and other well-known hate groups, but recently . has expanded its list to include such organizations as the Center for Immigration Studies (which advocates very limited immigration) and the Family Research Council (a pro-marriage, pro-life group), drawing complaints of political bias from critics.

"The terms are not legal terms, they are political terms, and therefore are subject to political bias," says Cornell Law School professor William A. Jacobson.

"That political bias in using the terms is clear at SPLC, which overwhelmingly applies the terms to groups it considers 'right wing.' This has a very chilling effect on political speech when used by a well-known entity like SPLC, because the labels are then used to try to prevent appearances on campuses, and even to disrupt or shut down appearances," Jacobson says.

Beirich says it's not a group's political agenda that earns them a space on the SPLC's list of hate groups, it's whether a group seeks to "demonize an entire population based on their inherent characteristics." The Family Research Council, she says, is on the list not because it opposes same-sex marriage, but because its leaders have claimed gay men are more likely to be criminals or pedophiles. The Center for Immigration Studies, she says, is considered a hate group because it has distributed propaganda from a Holocaust denier.

Hate speech, Beirich says, is a much tougher concept to define, and other experts caution against throwing the term around too casually.

"What people are really concerned about is, when does hate speech have the potential to lead to violence? That's' a tricky question to answer," Beirich says.

"When we think about language, we need to protect the meaning we attach to words" so their power is not diluted, says Kathleen Hall Jamieson, director of the Annenberg Public Policy Center at the University of Pennsylvania and an expert on political rhetoric. Calling something a "hate group" or "hate speech" is "identifying something we should flag and object to strongly," she says. If overused, "you're going to exhaust the capacity of language to express outrage."