WASHINGTON — They both wore the uniforms of their country during congressional testimony, but Alexander Vindman struck the reverse image of Oliver North.

Thirty-two years ago, North — then a Marine lieutenant colonel on the National Security Council staff — testified before Congress about his role in defying Congress to deliver aid to Nicaraguan rebels. On Tuesday, Vindman, currently an Army lieutenant colonel on the National Security Council staff, told House impeachment investigators that it was "improper" for President Donald Trump to "demand a foreign government investigate a U.S. citizen and political opponent."

Had Vindman stood alone — under attack as he was from Trump, Donald Trump Jr. and other allies of the president — he would have made for a compelling accuser.

But later in the day, his conclusion was supported by two witnesses — former special envoy to Ukraine Kurt Volker and former National Security Council staffer and longtime GOP Hill aide Tim Morrison — who said that it was not "appropriate" for a president to ask a foreign leader to investigate an American citizen, particularly one, former Vice President Joe Biden, who is a political rival of the president.

In the end, Vindman was just the most riveting of four witnesses who delivered testimony that was deeply damaging to Trump's remaining defenses against allegations that he was personally involved in pushing for an arms-for-investigations deal.

Taken together, over nearly a dozen hours, they testified to the direct access that Ambassador to the E.U. Gordon Sondland had to Trump as Sondland, Rudy Giuliani, the president's personal lawyer, Volker and others operated a special channel of Ukraine negotiations in which the investigations of Biden and his son were discussed.

They testified that chasing Biden for political advantage was neither consistent with established U.S. foreign policy goals nor consistent with appropriate conduct by the president. And Volker dismissed the probes sought as "conspiracy theories."

For Republicans, Vindman's willingness to contradict the president, the fact that he emigrated from Ukraine with his family as a toddler and the fact that Ukraine had sought to name him defense minister — an offer he had refused — were all reasons to question his loyalty to the United States. For Democrats, they were reasons to celebrate his patriotism.

"Lt. Col. Vindman brought receipts," Rep. Eric Swalwell, D-Calif., a member of the Intelligence Committee, wrote in a tweet directed at Rep. Jim Jordan, R-Ohio. "You can keep smearing a decorated war hero, but he brought his performance review today."

The other witnesses — Volker, Morrison and Jennifer Williams — were expected to provide testimony helpful to the president.

They did not.

It was bad enough that the main question multiple Republican lawmakers had for witnesses was whether they had observed others committing acts of bribery, extortion or treason — questions that both called upon the witnesses to act as juries and could have exposed them to legal jeopardy had they answered in the affirmative.

Williams described the key July 25 phone call between Trump and Ukrainian President Volodymyr Zelenskiy as "unusual," adding that Trump's request for Zelenskiy to investigate Joe Biden "struck me as political in nature given that the former vice president is a political opponent of the president."

Volker began his testimony by revising what he'd said to the lawmakers behind closed doors during an earlier session, and portraying himself as having been duped by his colleagues.

He said he did not understand originally that when they talked about investigating Burisma — the natural gas company on whose board Hunter Biden sat — that they intended for a probe to be launched into the former vice president.

"There's a way to thread that needle," he said he thought. But, after seeing the record of the president's July 25 call, he testified, he realized that "for them, it was synonymous."

"In hindsight, I now understand that others saw the idea of investigating possible corruption involving the Ukrainian company, 'Burisma,' as equivalent to investigating former Vice President Biden," he said. "In retrospect, I should have seen that connection differently, and had I done so, I would have raised my own objections."

Morrison said that he "was concerned" about Sondland connecting aid to investigations in a conversation with Ukrainians, that Sondland briefed Trump on the July 25 call and that Sondland repeatedly spoke to Trump directly.

Morrison also testified that he wanted to limit the number of people who had access to a record of Trump's call with Zelenskiy because he was was worried that if it leaked there would be political ramifications in the U.S. The fear: that it would threaten bipartisan support for Ukraine. At the time, though, Trump had frozen the money Congress had appropriated for Ukraine.

"I was interested in locking down the transcript," he said — but he also testified repeatedly that he saw nothing wrong with anything the president had said on the call.

That may be hard for Americans to square with Morrison's acknowledgment that it's not right for the president to seek an investigation into a political opponent.

So much for helping Trump. The takeaway from Morrison's testimony will be the same as Vindman's: Trump's conduct was inappropriate.