This is smart. The Trump campaign needs to do the and seriously spread this through their surrogates or through Trump himself.
If you frame it as "BLM's campaign of intimidation" or something along those lines, this will do two big things, with the latter being more important for Trump:
1. You severely blunt BLM's effectiveness by calling the violence beforehand and making people aware that they will do this. As a result, BLM will either seriously back off of their plans or take a severe hit in public perception if they do.
By calling it upfront and BLM proving them right, it will seriously blunt the ability for the media to push the narrative that BLM are these activist freedom fighters, and without the media propping them up, their actions will be seen as the brutal partisan thuggery that it truly is. Most people already don't like BLM but are unable to speak out due to it going so against the media narrative, which gives shitlibs the supposed moral high ground to bully the majority into submission.
Or, they realize that this would be political suicide and BLM backs down, which further creates divisions on the left, because then the left fights over why BLM didn't go protest the new Hitler.
It's also an easy prediction to excuses away if it doesn't happen. Just say something like "Based on the events in the past few months regarding BLM, preparations were made bythe RNC, the City of Cleveland, and the Trump campaign to protect the convention from likely violent protest."
2. Doing this severely limits the ability of GOP officials and other party members from gathering any public support for any anti-Trump efforts, as well as ensuring that the blowback from any of these efforts will be extremely toxic to any who try.
It creates and highlights a convergence of goals between any in the GOP that would screw over Trump and the BLM thugs outside that doesn't even really need to be explained to most, but will be easily understood if verbalized.
This creates a sort of "you're either for us or for them" effect, and since BLM is so hated among the right, this will seriously blunt any effectiveness from those who want to pull some shit at the convention.