US President Donald Trump. File photo

As impeachment hearings play out in Washington, high-level officials, many of them immigrants or children of immigrants, who have testified before Congress are being forced to defend their loyalty to the United States.

Ukrainian-born Lieutenant Colonel Alexander Vindman, a National Security Council expert, rebuffed attacks by proudly stating at the proceedings: "The uniform I wear today is that of the United States Army."

Like many of his peers who have testified, he embodies the "American Dream," as an immigrant who rose to the top.

Having displayed exemplary service to their country, they boast of patriotic gratitude for the United States, which gave them opportunity -- and for some, refuge from oppression.

But that attitude has given them little cover from attack as they participate in the impeachment investigation against Donald Trump, spurred by a phone call in which he asked Ukraine to investigate one of his potential 2020 presidential election opponents.

Vindman, whose family fled anti-Semitism in the Soviet Union to New York when he was just three, has been subject to sharp criticism from the president and his allies.

As a respected member of the White House National Security Council, he testified before the House Intelligence Committee on Tuesday wearing his dress blue uniform displaying his combat infantry badge, campaign ribbons and a Purple Heart received for wounds suffered by a roadside bomb in Iraq.

Following his testimony, which touched on the pressure the president's cohorts had placed on Kiev, Trump cast doubts on his allegiance.

One guest commentator on the conservative TV channel Fox News even accused him of being a spy for Ukraine.

During the hearing, an attorney for the House Republicans questioned him at length about the fact that a Ukrainian official had offered him the position of minister of defense in Kiev. Vindman explained that he never knew if the offer was serious and immediately declined.

Repeating multiple times that he is an American, he told the Intelligence Committee that "as a young man I decided that I wanted to spend my life serving the nation that gave my family refuge from authoritarian oppression."

Agence France-Presse