Of course they are mad. The Republican strategy up until this point has been to attack the incumbent, but now the incumbent is no longer running for re-election. Trump literally doesn’t know how to deal with this situation. His whole shtick is to attack the person currently in charge, but that doesn’t do shit for him now.
A big part of why he lost in 2020, imo, is that he didn’t have anybody to blame for all the bad shit happening in the country at the time. He himself was in charge and could only say “things will get worse under Biden”, but people were sick of Covid fucking up our lives and the endless scandals that hit the news daily.