Casey is up +13 in the latest poll.
If you look at trends, right now Casey is trending downwards from +18 in April to +13 in the latest. Its gonna take a bit more closing of the margins before one can get nervous about Casey losing his seat.
https://www.realclearpolitics.com/epolls/2018/senate/pa/pennsylvania_senate_barletta_vs_casey-6312.html