The fourth anniversary of the Tree of Life massacre took place this week. The attack on the Jewish community was the worst in US history.

A rant blaming a Jewish American group that provides aid to refugees for bringing violent invaders in that would kill was one of the antisemitic slurs posted by the suspected white shooter.

The baseless idea that there is a plot to weaken the influence of white people in America has been peddled by some mainstream Republican candidates.

There used to be consequences for engaging in white supremacist rhetoric, but that is no longer the case, according to the Global Project Against Hate and Extremism co- founder.

The idea that it's connected to mass killing is astounding. Is it possible for a politician to push a belief when it's connected to terrorism? This is terrorism right here in our country.

The Anti-Defamation League's Center on Extremism and Yahoo News spoke about the dangers of the great replacement theory and how it made its way into mainstream politics. Responses have been edited for clarity.

There is a great replacement conspiracy theory.

The great replacement theory is a white supremacist idea that there is a plan to replace white populations in their home countries with people of color. Depending on where you are in the world, that could be a Muslim, a refugee, or a Latino.

This is seen as an orchestrated plot, so there is something being done to wipe out white people in what they consider their countries.

The theory came from somewhere.

The idea of a great replacement has been around for a long time, but the most recent iteration was written by a French writer, called "The Great Replacement." He was writing about immigrants from Africa and the Arab world. White nationalists all over the world were influenced by this essay.

It's important to point out that there are different versions of the same thing. When he wrote about the great replacement, he didn't mention Jews. He did not talk about the Jewish population. There are some people in the white nationalist or white supremacist movement who do not like Jews.

There is an antisemitic version of the great replacement, in which Jews are blamed for bringing nonwhite immigrants into the US and Europe. The idea that Jews control world situations, or they're trying to manipulate situations to their advantage, and that they would bring in all these nonwhite immigrants with the idea that they would control them is based on antisemitic stereotypes.

There is a third version of the great replacement that is being used by more mainstream figures but still on the right side. This version has something different to it. It's not antisemitic, but what it says is that Democrats and the left are trying to bring immigrants from nonwhite countries. They are doing this through borders. The reason they're doing this is so that immigrants will vote Democratic and replace traditional Americans.

The great replacement theory is not safe.

A number of murderers have been inspired by the great replacement theory. The inspiration for many of the people who came after him was the fact that he killed 77 people because he was against immigration.

I'm talking about the people who came after him, including the person who killed people in a mosque in New Zealand, the person who killed people in a Walmart in El Paso, and the person who killed people in Buffalo.

The great replacement theory has been promoted.

The idea of a great replacement is being mainstreamed by many different people. White Christian America is losing out due to the influx of immigrants because they don't feel like they can adapt to American culture. It's been weaponized because it's being talked about by pundits and politicians and they are going to take either your position, your job or something away from you, and therefore you need to fear.

There may be legitimate issues around immigration and about the country absorbing a large number of immigrants, but that's not the same as saying that there's a plot to actually get these people to come over here and vote a certain way and control the country. That is what makes it a conspiracy theory.

Tucker Carlson of Fox News has endorsed the replacement theory a number of times. Tucker Carlson blamed Democrats for engaging in replacement after the Buffalo mass shooting.

The way that the great replacement has become so mainstreamed in terms of an electoral strategy for candidates goes back to Donald Trump making the decision to take on Latinos, take on immigrants, and also throughout the entire time that he was running for president. Some of the harsher immigrant measures were put in place by him. Stephen Miller, who had relationships with white supremacists, was one of the advisers he had.

They injected a race issue into the campaigns. Conservatives are using this as a way to mobilize their base, by demonizing immigrants, and using the great replacement theory to argue that there is some sort of plot involved with people coming here.

This kind of white supremacist hate has never been mainstreamed like this in the 30 years I've been looking at extremists.

The conspiracy theory may have been normalized.

According to the polling done by the Southern Poverty Law Center, close to 70% of Republicans believe that the replacement is being orchestrated by liberal elites, meaning either wealthy people like George Soros or people who have become bogeymen on the right.

The kind of rhetoric that we've seen from people with massive audiences starting in 2015 is not surprising. In June 2015, when Trump spoke about Mexicans and referred to them as rapists, it was the beginning of the end of that rhetoric.