Former Rep. Gabrielle Giffords (D-Ariz.) and former Sen. Jeff Flake (R-Ariz.) called for an end to political violence in an USA Today opinion piece that came in the wake of conservative activist Charlie Kirk’s death.

“There are calls for ‘war’ targeting progressive institutions and donors, and other frightening forms of collective punishment against the president’s critics,” Giffords and Flake said in the opinion piece, published Saturday.

“Meanwhile, there are radical individuals on the left celebrating the tragedy as an act of twisted political justice. Political violence of any kind, waged by government agents or external extremists, is a betrayal of our founding principles,” the two added.

Kirk was shot and killed last week while responding to questions from students at an event at Utah Valley University. Following a manhunt, law enforcement, officials identified the alleged suspect as Tyler Robinson, 22, of Utah.

Giffords, whose husband is Arizona Sen. Mark Kelly (D), was shot in the head and nearly killed during a meeting with constituents in 2011. The man who shot Giffords and killed six other people had an extensive history of mental illness.

“If we Americans allow ourselves to be dragged further down this path of violence and retribution, we will lose ourselves – and our country,” Flake and Giffords said in their piece.

“We will abandon the pursuit of a more perfect union and descend into a frightening era where neighbors are suspicious, strangers are enemies and political opponents are threats who must be neutralized,” the two added.