Sen. John Fetterman, D-Pa., says the U.S. has to "turn down … the temperature" following President Trump's attempted assassination at a rally on Saturday. 

The senator referred to the shooting as a "dark day" and "tragedy" during an interview with CNN's "State of the Union" on Sunday morning. 

Fetterman said it might be necessary for Congress to investigate what, if anything, went wrong from a security standpoint during the Trump rally on Saturday. 

"We can't assume that these kind of things can't happen again," Fetterman said. "We just have to turn down … the temperature on this. And this election is going to be the biggest kind of election in our lifetime, and we have months ahead of us."

He added: I'm not gonna make it about politics."

FORMER PRESIDENT TRUMP SURVIVES ASSASSINATION ATTEMPT, FBI IDS SHOOTER AS THOMAS MATTHEW CROOKS

Democratic Pennsylvania Sen. John Fetterman

Sen. John Fetterman, D-Pa., leaves an intelligence briefing on the unknown aerial objects the U.S. military shot down this weekend at the Capitol in Washington, Feb. 14, 2023.  (AP Photo/J. Scott Applewhite, File)

The Democratic Senator said he was in the region near the outdoor rally venue in Butler, Pennsylvania, when it happened Saturday evening, to attend a vigil for a transgender teenager who had been murdered.

Americans fear rising political violence, recent Reuters/Ipsos polling shows, with two out of three respondents to a May survey saying they worried that violence could follow the election.

REPUBLICAN NATIONAL CONVENTION SECURITY TIGHTENS FOLLOWING TRUMP ASSASSINATION ATTEMPT

Donald Trump gestures while surrounded by U.S. Secret Service agents

Republican presidential candidate former President Donald Trump gestures while surrounded by U.S. Secret Service agents as he is helped off the stage at a campaign rally in Butler, Pa., Saturday, July 13, 2024.  (AP Photo/Gene J. Puskar)

Trump supporters cheers as the American flag is untangled before former US President and Republican presidential candidate Donald Trump speaks during a campaign event

Trump supporters cheer as the American flag is untangled before former U.S. President and Republican presidential candidate Donald Trump speaks during a campaign event at Butler Farm Show Inc. in Butler, Pennsylvania, July 13, 2024. Donald Trump was hit in the ear in an apparent assassination attempt by a gunman at a campaign rally on Saturday, in a chaotic and shocking incident that will fuel fears of instability ahead of the 2024 U.S. presidential election.  (Rebecca Droke/AFP via Getty Images)

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Fetterman said he is grateful that Trump is making a full recovery, is thinking about the rally attendee killed and hopes the two people who were critically injured will be okay. 

"My drive back home last night from northwestern Pennsylvania … I was just incredibly sad," he said. "I just can't believe that this is the place where our nation is."

Reuters contributed to this report.