As Congress moves forward with a formal impeachment inquiry of President Trump for asking Ukraine to investigate his political rival, the White House is fighting back by refusing to cooperate. Now, subpoenas are dropping left and right. But what are congressional subpoenas and how will they work in the Trump era? Experts aren’t sure what lies ahead.

What is a subpoena?

Subpoenas are orders to produce records or testimony. They are issued by courts and government agencies, and failure to comply can result in civil or criminal penalties.

What is a congressional subpoena?

Congress has broad authority, established by Supreme Court rulings, to oversee the executive branch and conduct investigations. As part of these powers, Congress can request documents or ask witnesses to testify. While not specified by the Constitution, Congress has a long-established history of using subpoenas to compel testimony when information is not provided voluntarily.

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What happens if someone defies a congressional subpoena?

The longstanding — though unofficial — approach is for subpoenaed individuals or agencies to negotiate terms of compliance, said Lisa Kern Griffin, a professor of constitutional law at Duke University. For example, Congress in the past has worked out compromises with an administration to provide some witness testimony or redacted evidence. This option is basically a non-starter in the Ukraine case, Griffin said, because the Trump administration has said it does not intend to cooperate.

Congress has three options to enforce subpoenas in face of defiance, but none are particularly appealing for lawmakers. Congress could pursue criminal contempt by asking the U.S. Attorney for D.C. within the Justice Department to bring criminal charges against a violator. If found guilty, this would be a federal misdemeanor punishable by a maximum $100,000 fine and a maximum one-year sentence in prison, said Margaret Taylor, a former Democratic Chief Counsel for the Senate Foreign Relations Committee.

But this is not a viable option; it’s improbable that the Trump Justice Department would bring criminal charges against a member of its own administration. During Barack Obama’s presidency, the House voted to hold former Attorney General Eric Holder in contempt of Congress in 2012, but the DOJ chose not to prosecute. Another possible remedy is for Congress to file a civil lawsuit in federal court, requesting a judge to order compliance with the subpoena. This, however, can take months or years to resolve. The third alternative is for Congress to use its own “inherent contempt” power by sending the Sergeant at Arms to actually detain subpoena violators. But this hasn’t been done since 1935, and is widely viewed as an extreme option, said Taylor.

Who have lawmakers subpoenaed in the Ukraine investigation?

A number of investigations began prior to the announcement of a formal impeachment inquiry. Since the Ukraine probe began, House committees have subpoenaed the White House, State Department, Office of Management and Budget, Department of Defense, U.S. Ambassador to the European Union Gordon Sondland and Energy Secretary Rick Perry.

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Is there anything unusual about the Trump administration’s response?

Push and pull between the executive and legislative branches is typical, Taylor said, but what is unusual is the current administration’s staunch refusal to cooperate, she added. The administration’s stonewalling in the Ukraine probe, paired with its lack of cooperation since Democrats took control of the House, underscore Congress’ limited options. These present challenges for a government system that often “relies on the good faith” of individuals, Griffin said.

“The government in many respects is held together by norms and customs and unwritten rules, Griffin said. “Probably the clearest lesson of the Trump era is that unwritten rules don’t work when they run up against bad faith.”

So, what will House lawmakers do?

One option is for the House to avoid the courts and instead use the administration’s noncompliance as further evidence for articles of impeachment against the president. “The failure to produce this witness, the failure to produce these documents, we consider yet additional strong evidence of obstruction of the constitutional functions of Congress,” House Intelligence Committee Chair Adam Schiff said to reporters on Tuesday.