An early public test of Democrats’ newfound power to investigate President Trump and his administration may take place Friday — if acting Attorney General Matthew Whitaker testifies before the House Judiciary Committee about his role supervising special counsel Robert Mueller’s investigation into Russian interference in the 2016 election.

Whitaker had initially agreed to testify voluntarily but now says he won’t appear unless the Democrats agree not to use their subpoena power to compel him to answer questions. But Democrats have no shortage of topics to grill Whitaker about. His qualifications and impartiality regarding the Mueller probe — which he has publicly criticized in the past — were immediately questioned when Trump announced that Whitaker would temporarily take over for ousted Attorney General Jeff Sessions in November. And in late January, Rep. Jerrold Nadler, chairman of the House Judiciary Committee, sent Whitaker a list of questions that he plans to ask during the hearing, including whether Whitaker passed on information about Mueller’s investigation to Trump or Trump’s private legal team.

In his State of the Union address on Tuesday, Trump called for an end to “ridiculous partisan investigations,” in what seemed like a clear warning to Democrats. As I wrote last month, there’s evidence that congressional investigations have eroded past presidents’ approval ratings. But there are also plenty of ways that congressional Democrats could falter, by either failing to unearth the truth at the heart of whatever it is they’re looking into or to grab the public’s attention and land political punches.

Investigators need to avoid getting lost in the details

Congressional investigations are inherently theatrical. But political science experts told me that Democrats shouldn’t expect to win over the public by simply producing new facts — instead, they need to contextualize whatever information they find within a simple, compelling story.

“If the narrative were corruption, let’s say, they could try to draw in a lot of different Cabinet officials, make it bigger than the president, but still keep it cohesive,” said Josh Chafetz, who is a law professor at Cornell University and studies the relationship between Congress and the president. “The danger is that if you make it sound like it’s 40 disconnected issues, people lose track and tune out.”

This means that if Democrats begin questioning Whitaker on Friday, they may have more success if they can use their questions to hammer broad, overarching themes, rather than to focus on details. For instance, Democrats may be tempted to pepper Whitaker with queries about his past business dealings, but they might be better off sticking to questions that will keep the public’s attention on potential attempts by Trump to interfere with the Mueller investigation — a line of inquiry that Mueller himself seems to be following.

The White House has tools to resist

The Democrats will also have to pick their battles carefully, since the White House has a variety of ways to slow down or thwart their investigations. One is for Trump to claim executive privilege — a power that the president can invoke to withhold information — to prevent a witness, like Whitaker, from answering certain questions. Another is to refuse to turn over documents or defy subpoenas. Whitaker didn’t meet the deadline set by Nadler to inform the committee about whether the president would invoke executive privilege ahead of Friday’s scheduled hearing, so the committee authorized a subpoena to compel Whitaker to respond to questions if he refuses to discuss his oversight of the Mueller investigation. Whitaker’s threat to refuse to testify could prompt the Democrats to use that subpoena power earlier than expected — potentially setting up a showdown with the White House.

When an administration fights back, Congress does have some mechanisms for responding, but they’re imperfect, according to Lance Cole, who is a law professor at Penn State Dickinson Law and was a deputy special counsel for the Democrats on the Senate special committee tasked with investigating the Whitewater scandal, which involved a land deal made by Bill and Hillary Clinton in the 1970s. For example, he said, Congress can authorize contempt charges against someone who has refused to respond to a subpoena, but the Justice Department ultimately decides whether to prosecute that person. Another option is for Congress to file a civil lawsuit, but that process is extremely slow.

The result, Cole said, is that House Democrats need to weigh the costs of a protracted fight with the White House when they decide which information to go after. In Whitaker’s case, if he refuses to answer certain questions or Trump claims executive privilege, Democrats will have to determine whether it’s worth wrangling with Trump over what he’s legally obligated to reveal.

The public may be less persuadable

Another potential roadblock for House Democrats as they try to hurt Trump politically is the fact that he’s already pretty unpopular. Even though congressional investigations have damaged presidents’ public standing in the past, Trump’s low job approval ratings could mean that there just aren’t many people left to convince to abandon him. And House Democrats may struggle to simultaneously appeal to those voters and rank-and-file Democrats, who are eager to take down the president. This creates a bit of a double-edged sword for House Democrats: Hearings that seem to be motivated by partisanship, rather than specific facts that point to potential wrongdoing, could undermine their credibility, but if congressional Democrats move too slowly, or appear to be hesitant, they could end up being criticized by their own base.

The timing of subsequent hearings could also be crucial. Political scientist Eric Schickler of the University of California, Berkeley, told me that stretching out hearings so that different committees don’t step on one another’s toes may help boost and sustain media coverage, which can be important for helping an investigation gain traction.

The Whitaker hearing, if it happens, as well as how quickly more hearings featuring Trump administration officials take place, could give us some clues about the kind of balance Democrats are trying to strike. But this is the beginning of a long process, so Democrats’ ability to recognize and learn from any mistakes they make in these early stages may be just as important.

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