Remember the Democrats’ newfound subpoena power? Turns out, it’s actually a double-edged sword. If Democrats begin summoning people to testify who are witnesses in or targets of the special counsel investigation, they could derail key parts of Mueller’s strategy. The most disruptive step Democrats could take would be to offer immunity to people Mueller is still in the process of questioning or prosecuting. And it has happened before: As part of its Iran-Contra investigation, Congress offered immunity to two former Reagan administration officials — John Poindexter and Oliver North — in exchange for their testimony about secret arms sales to Iran. The decision, which was strenuously opposed by the Iran-Contra independent counsel, ultimately resulted in both convictions being thrown out.
But let’s say immunity isn’t on the table. Holding public hearings with people who are in Mueller’s orbit could still cause problems for the special counsel, according to Katy Harriger, a political science professor at Wake Forest University who studies the history of independent counsel investigations. “There’s this perennial tension between congressional investigations and special prosecutors because Congress’s goal is to shed light on everything, while it’s much better for Mueller to keep what he’s doing secret until he issues his indictments,” she said.