Bernie Sanders has condemned the man who shot several people, including a fellow political figure, at a baseball stadium in Virginia.
Among those injured were capitol police and Republican majority whip Steve Scalise.
Sanders said in a statement that the man "apparently volunteered on my presidential campaign".
He went on to say that he was "sickened and disgusted by this despicable act".
The shooter, who died soon after the attack, was named as James T Hodgkinson from Illinois.
Sanders has been a vocal critic of US gun laws and said that "violence of any kind is unacceptable in our society".
Scalise was hit in the hip around five times when more than 50 shots were fired from a rifle. He was training in Virginia ahead of a charity baseball game.
The Republicans were training at the grounds in the run up to the 56th annual Congressional Baseball Game, which was set to take place tomorrow.
According to NBC, the congressional baseball game will be played tomorrow night as scheduled,
In 2016, Republicans beat the Democrats to win the game, breaking a seven-year winning streak by the Dems.
Former Arizona congresswoman Gabrielle Giffords tweeted her support to those injured in the attack.
In 2011, she was shot in the head while six others were killed. Scalise is the first sitting congressman since Giffords to be shot.
She said: "My heart is with my former colleagues, their families & staff, and the US Capitol Police- public servants and heroes today and every day."