Former U.S. Ambassador to Ukraine Marie Yovanovitch Marie YovanovitchStrzok: Trump behaving like an authoritarian Powell backs Biden at convention as Democrats rip Trump on security Marie Yovanovitch appears in Democratic convention video ripping Trump MORE, a central figure in the House impeachment of President Trump Donald John TrumpBarr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' Military leaders asked about using heat ray on protesters outside White House: report Powell warns failure to reach COVID-19 deal could 'scar and damage' economy MORE, on Thursday warned the public against allowing the U.S. to become a country that silences those who stand up to the government.

In an op-ed published in The Washington Post, Yovanovitch recalled how she and other civil servants spoke out last year when they believed the Trump administration was committing wrongdoing in its dealings with Ukraine.

She added that they also testified before Congress because they believed that speaking up about impropriety is the "American way."

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"I have seen dictatorships around the world, where blind obedience is the norm and truth-tellers are threatened with punishment or death," Yovanovitch wrote. "We must not allow the United States to become a country where standing up to our government is a dangerous act. "

After nearly 34 years working in the State Department, Yovanovitch retired last month. Her departure came months after she was recalled from her role as the ambassador to Ukraine following a targeted campaign from President Trump and his lawyer, Rudy Giuliani Rudy GiulianiJuan Williams: Breaking down the debates Giuliani criticizes NYC leadership: 'They're killing this city' More than 160 executives critique de Blasio's leadership amid pandemic MORE.

She testified before lawmakers in November that Giuliani and his associates had orchestrated an effort to push her out of her position, alleging that they were behind unfounded attacks against her.

Yovanovitch said that it has been "shocking" to see the "criticism, lies and malicious conspiracies that have preceded and followed my public testimony." But she asserted that she had no "regrets" about testifying before Congress, noting that "I did — we did — what our conscience called us to do."

"We did what the gift of U.S. citizenship requires us to do," she said.

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She denounced the current administration as one that "has undermined our democratic institutions" and left public servants without the support necessary to sufficiently complete their jobs and advance U.S. interests.

"The next generation of diplomats is counting on something better," she wrote, adding later that while the events of the past year were "deeply disturbing," she's optimistic that the U.S. will "prevail."

Yovanovitch became the fourth figure to depart from the State Department after being tied to the House impeachment inquiry, which focused on Trump's alleged push to coax Ukraine into announcing probes of his political rivals.

Trump and Giuliani have repeatedly denied any wrongdoing, though Giuliani has acknowledged telling Trump that Yovanovitch was blocking requests for investigations into 2020 presidential hopeful and former Vice President Joe Biden Joe BidenThe Memo: Warning signs flash for Trump on debates Senate Republicans signal openness to working with Biden National postal mail handlers union endorses Biden MORE.

New evidence released in January has also raised concerns that Yovanovitch may have possibly been surveilled as Giuliani's associates pushed for her ouster. The State Department has since announced an investigation into those allegations.

The Senate on Wednesday voted to acquit Trump of impeachment articles stemming from the House's probe into the president's dealings with Ukraine.