Susan Collins said threats against members of congress could lead to physical violence.

Collins told The New York Times that he wouldn't be surprised if a lawmaker were killed. Abused phone calls are now turning into threats of violence.

Lawmakers of both parties have been the target of threats. According to data from the Capitol Police, the number of threats against members of Congress has gone up a lot over the past few years.

In October of last year, Collins received a threatening letter from a woman who was upset that he voted to confirm the Supreme Court justice. Someone sent Collins a video of a beheading and a threat to kill her, according to The Times.

Collins told the outlet that someone smashed a storm window on a tucked away part of her house.

"There's been a sea change in that we now see this constant escalation and erosion of any boundaries of what is acceptable behavior, and it has crossed over into actual violence." She said that three people are in prison because of threats made against her.

Some members of congress have received death threats.

Some members of Congress have been attacked with violence.

Giffords was shot in the head outside a grocery store. A Republican congressman was shot during a baseball practice.

Several dozen people have been arrested for threats against lawmakers in the last three years. The majority of threats come from people who are mentally ill.