One after the other, suspicious packages were delivered to the media and liberal leaders, many in New York City.

"This is a very painful time in our nation. It's a time when people are feeling a lot of hate in the air," said Bill de Blasio, (D) New York City Mayor.

Some are calling it domestic terrorism and others call it political terrorism.

"Someone one who might be trying to  use scare tactics or trying to enhance political passions, make partisan divisions worse," said Corri Zoli, National Security and Counter-Terrorism Research Director.

It is a scary thought for a country largely functioning on a two-party system.

Zoli said, "It's not accurate to characterize opposition groups as enemies in a two-party system that structures the United States."

But, is that what we're seeing?

In 2017, the target appeared to be on the other side of the aisle, members of Republican Congressional baseball team.

"Is this a retaliatory attack for those attacks? This is the problem with polarization. You get these kind of escalating dynamics...clearly this is an expression of partisanship gone awry," said Zoli.

The US has seen in the past, but it's rare. 

The country has always been strategic in the way it carries out political differences.

"We take our grievances or our differences, our debates, our conflicts to the ballot box. We don't fight out our political differences through violence. We don't do that. Many many countries in the world do exactly that and have very very unstable political culture because of that. We don't do that. it's a very worrisome trend to see these kinds of outcroppings of political violence and it's also worrisome to see political leaders and thought leaders and they should know better even joking about political violence being an option," said Zoli.

Now, the question is how do you stop it.

Zoli said it's up to the public to speak up against these acts of violence.