Mitch McConnell wants someone to murder his challenger Amy McGrath

This photo comes from a Mitch McConnell rally in Kentucky held about the same time as the El Paso shootings.  The names on the tombstones are people who have challenged McConnell.  The tombstone in the right front corner is inscribed to Amy McGrath, who is challenging McConnell in 2020.

Why has McConnell not been arrested for soliciting murder?