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.
So far, Mueller has been extremely successful at keeping the details of his investigation quiet. Reporters track the comings and goings of witnesses at his grand jury, but the details of what Mueller has learned and his overall strategy remain a mystery to observers, including the people who may be implicated. But public hearings could change this dynamic completely, allowing witnesses to coordinate with each other about the story they’re telling investigators. Congressional hearings could also produce testimony that conflicts with Mueller’s findings.
Communication with Mueller’s team could help the Democrats avoid some of these problems, but Barrett said that it might be better for them to avoid bringing in high-profile witnesses until Mueller’s investigation is complete. Instead, Democrats could start by subpoenaing documents and financial data that shed light on the events of 2016 without requiring someone like Roger Stone — the former Trump campaign official who claimed to be a pipeline to WikiLeaks — to testify publicly.
But if history is any indication, Mueller might want to brace himself for unwanted interference. “The Democrats will want to tread carefully, because we’ve had a long history of congressional investigations that were at cross-purposes with independent counsel investigations,” said Rosenzweig. However, legal experts like Rosenzweig say that there are many avenues that House Democrats can pursue that won’t step on Mueller’s toes, like investigating whether Russia has leverage over Trump’s financial interests.
In the end, if Democrats don’t want to disturb or undermine Mueller’s work, the best course of action might be the simplest (and one they’ve advised Trump to take many times over the past 18 months): Leave Mueller alone.