Mueller knows there's no way he can actually get these Russians into a courtroom. Consequently, there 's no reason why he could not have waited on the indictments until after the summit meeting. The announcement of these indictments a few days before President Trump's meeting with Putin was designed to sabotage the summit and try to make President Trump as uncomfortable as possible going into the meeting.
“Mueller knows there’s no way he can actually ...”
You helped me realize that “sealed” indictments means indictments whose existence aren’t made public, not just that the contents of the indictments aren’t made public.