Congressional investigators expect that Marie Yovanovitch, the former ambassador to Ukraine, will appear as planned for a Friday deposition in the House’s ongoing impeachment inquiry, despite the White House’s emphatic pledge not to cooperate with Democrats’ efforts to investigate President Trump, according to congressional officials involved with the process.

Yovanovitch and her lawyer are “on board,” according to a senior congressional aide, who like others spoke on the condition of anonymity to discuss sensitive negotiations. Yet House Democrats are preparing backup options to facilitate her testimony — including issuing a possible “friendly” subpoena, according to two people involved in the investigation — in case the State Department forbids her from speaking to lawmakers.

Last week, State Department officials blocked the U.S. ambassador to the European Union, Gordon Sondland, from testifying before the panels at 12:30 a.m. on the morning of his planned testimony, prompting the panels to subpoena him. State Department officials would not address questions about Yovanovitch on Wednesday, and efforts to contact her were unsuccessful.

White House lawyer Pat Cipollone issued a letter to Democrats on Tuesday outlining the Trump administration’s objections to the impeachment inquiry, calling it unconstitutional and vowing to reject congressional requests to cooperate.

House Democrats dove into October with plans to depose a roster of current and former State Department officials, affiliates of the president and his personal lawyer Rudolph W. Giuliani — individuals who helped or were privy to efforts to influence Ukrainian leaders to conduct investigations that could damage Trump’s political rivals.

Thus far, they have deposed only Trump’s former special envoy to Ukraine, Kurt Volker, who resigned his post late last month and then provided the committees with copies of text messages he exchanged with other diplomats, Giuliani and a top aide to Ukrainian President Volodymyr Zelensky.

Those messages revealed an apparent effort to encourage the Ukrainians to investigate the 2016 U.S. election, 2020 Democratic presidential candidate Joe Biden and Biden’s son Hunter, who served on the board of a Ukrainian gas company while his father was vice president.

Yovanovitch, a career diplomat with three decades of experience, was ambassador to Ukraine until she was recalled in May after coming under attack from conservative media figures who alleged she was biased against Trump. State Department officials have said the accusations are baseless.

Lawmakers are expected to ask Yovanovitch about her interactions with Giuliani, Trump, and others pertaining to the investigations they sought.

Giuliani has embraced some of the unproven accusations against Yovanovitch, including a theory that she played a role in an alleged conspiracy orchestrated by liberal philanthropist George Soros to expose former Trump campaign chairman Paul Manafort’s Ukraine-related corruption. The president’s son Donald Trump Jr. referred to her on Twitter as a “joker.” And the president himself suggested she was biased against him, telling Zelensky she was “bad news,” according to a White House summary of their July 25 phone call in which Trump sought to enlist Zelensky’s help looking into the Bidens.

For many U.S. diplomats, she has become a symbol of the political pressures being applied to apolitical professionals working for the State Department. According to people familiar with the negotiations, Yovanovitch has been quite willing to testify about her experience — but if the State Department objects before Friday, she may have to do so under subpoena.

Following stints as the U.S. ambassador in Armenia and Kyrgyzstan, Yovanovitch was posted to Ukraine at the end of the Obama administration and focused on urging Ukraine to tackle its endemic corruption.

Yovanovitch was recalled from Kiev two months early from her three-year posting. She remains on the State Department payroll, working as a fellow at Georgetown University.

Her recall rankled many of her colleagues, who are disappointed that Secretary of State Mike Pompeo did not do more to shield the veteran diplomat from false insinuations that led to political pressure from the White House.

Earlier this year, conservative media outlets attacked Yovanovitch and George Kent, the deputy assistant secretary of state responsible for Ukraine, accusing them of trying to protect the Bidens from an investigation by Ukrainian prosecutors. Kent was scheduled to appear before the House committees on Monday, but the deposition never took place. To date, lawmakers have not announced that they will subpoena him.

Nevertheless, Democrats are expanding the list of current and former officials they want to depose.

Trump’s former Russia adviser has been asked to answer questions at a deposition Oct. 14 by the committees pursuing the impeachment inquiry. Fiona Hill, who left that job in August, was also asked to bring any documents or correspondence that could shed light on efforts to influence Ukraine.

Devlin Barrett contributed to this report.