How has the modern grand jury system in the United States evolved since the drafting of the Constitution?
Originally, the grand jury was developed as a way to check the unrestrained power of the ruling class, to give citizens the opportunity to investigate any alleged crime, and to make sure that the crime happened. These investigations were conducted in secret so as to minimize damage to the reputations of innocent people who were falsely accused by the powerful. That vision, contemplated by the framers of the Constitution, stands in stark contrast to the current political uses of the grand jury, in which prosecutors may subpoena activists and jail them for refusing to comply with the subpoena. Grand juries have now become an unbridled arm of the police and prosecution in ways that run contrary to its originally intended purpose.
The drafters never intended the grand jury to function as it does today. The grand jury imagined by the drafters of the fifth amendment did not involve a prosecutor and bears no resemblance to what we see today, where more than 99.9% of indictments sought are granted. Consider that it is more than six times as likely that you will be struck by lightning than that a federal grand jury will decline to indict.
The grand jury process used to act as an independent body of citizens, along the lines of a civilian police review board. Early grand juries acted independently, as investigations by citizens, ostensibly to protect citizens, not only from unjust indictments, but from unjust laws.
Today's grand jury is a dangerous relic that has evolved in ways that increase its power without increasing any protections against its misuse. A mockery of the institution that once stood against the whims of monarchs, grand juries have clearly transformed into something that violates the spirit, if not the letter of the law.