It’s now up to U.S. Supreme Court Chief Justice John Roberts to decide whether to block an order opening the way for former White House counsel Don McGahn to testify before the House Judiciary Committee.

Roberts would need the support of five fellow justices to stay a decision by U.S. District Judge Ketanji Brown Jackson opening the way for McGahn to testify about his involvement in the investigation into Russian election interference led by special counsel Robert Mueller as the effort to quash the subpoena wends its way through the court system.

Jackson ruled last week the Justice Department could not block McGahn’s testimony because “presidents are not kings” and are subject to oversight by Congress under the Constitution. She then issued an administrative stay at the Justice Department’s request but Monday declined to issue a long-term stay, saying delaying McGahn’s testimony would do “grave harm” to the committee’s investigation.

The Judiciary Committee Wednesday opens the next phase of the impeachment investigation as it considers articles of impeachment stemming from Trump’s interactions with Ukraine. The panel also could consider obstruction of justice charges stemming from Trump’s alleged efforts to stymie the Mueller investigation. McGahn reportedly prevented President Trump from firing Mueller by threatening to quit.

“This court has no doubt that further delay of the Judiciary Committee’s enforcement of its valid subpoena causes grave harm to both the committee’s investigation and the interests of the public more broadly,” Jackson, an Obama appointee, wrote in a 17-page opinion issued Monday.

The Justice Department, which is appealing her original ruling, had sought a long-term say while the case is adjudicated. A three-judge appellate panel was scheduled to hear the case Jan. 3. The Justice Department has said it is prepared to take the case to the Supreme Court.

“DOJ also does not, and cannot, deny that whatever additional information that the committee [and the public] might glean from McGahn’s live testimony will be lost if the Judiciary Committee does not have an opportunity to question him prior to any House vote on impeachment,” Jackson wrote.