At a rally in Springfield, MO last week, Scott Boston said, "we have to kill the Claire Bear".
That statement got the attention of U.S. Capitol Security.
Now the Senator has more protection in Washington D.C., as well as more police patrolling her home in Kirkwood, Missouri.
Boston said his comment was not meant to be taken literally.
"It was clearly an unartful use of my language at the time," says Boston. "I wasn't thinking about that when I was onstage at the political rally."
McCaskill has not commented on the statement.
So far, representatives from her Washington office have stayed silent on the issue.