Tester is in a tight race against GOP challenger Matt Rosendale. President Trump is making multiple trips to the state to stump for the Republican candidate.

Trump Jr. attacked Tester for challenging the nomination of Navy Rear Adm. Ronny Jackson to become the secretary of Veterans Affairs earlier this year; the president’s son didn’t explain why that would be an important issue to Montana voters.

Jackson, Trump’s former White House physician who notably gushed about the president’s excellent health after a checkup early this year, was accused anonymously by a group of current and former White House medical staff of creating a hostile work environment. The allegations included drinking on the job and improperly dispensing medication to White House staffers.

Tester, the ranking Democrat on the Senate Veterans Affairs Committee, led the opposition against Jackson, though there were bipartisan concerns about Jackson. Even Vice President Mike Pence’s doctor raised alarms about Jackson’s behavior, CNN reported at the time.

Still, Trump Jr. slammed Tester Friday for trying to “go after and ... assassinate with no proof, no basis, no nothing, a good man simply because my father wanted to elevate him and put him in charge of an organization,” The Hill reported.

“Where’s the accountability to Jon Tester who did that?” he asked. “That makes you a piece of garbage in my mind.”

Trump Jr.’s name-calling comes amid concerns that harsh and insulting language in politics could be radicalizing some individuals to commit violence. FBI officials arrested suspected mail bomber Cesar Sayoc Friday. They believe he mailed bombs to 14 Democratic politicians and other targets who have been harshly attacked by the president. The van in which Sayoc was living was plastered with photos of the president and images of his critics in crosshairs.