WASHINGTON — At the heart of the impeachment drama gripping the nation's capital is the question of whether President Trump’s attempts to solicit Ukrainian investigations of former Vice President Joe Biden for his role in the firing of a Kyiv prosecutor in 2016 and possible Ukrainian interference in the 2016 U.S. presidential election were ethical.

Both of those motives took major hits during Tuesday’s impeachment hearings, as witnesses dismissed them as conspiracy theories and irrelevant — at best — to U.S. interests.

“The allegations against the [former] Vice President [Biden] are self-serving and not credible,” said Kurt Volker, the former special envoy to Ukraine. “Raising 2016 elections, or Vice President Biden, or these things I consider to be conspiracy theories circulated by the Ukrainians … they’re not things we should be pursuing.”

“I don’t think pursuing these things serves the national interest,” Volker said in open testimony to the House Intelligence Committee, which is conducting the impeachment inquiry.

Volker testified that he did not consider himself to be engaged in pressuring Ukraine in a way that constituted bribery or extortion. But several other witnesses have told the committee that Trump withheld nearly $400 million in military assistance to Ukraine, as well as the prospect for a White House meeting with Ukrainian President Volydymyr Zelensky, in order to force Ukraine to announce investigations into Ukrainian interference and the Bidens.

Kurt Volker, former special envoy to Ukraine, testifies before the House Intelligence Committee on Tuesday. (Photo: Susan Walsh/AP)

Republicans have argued that one reason Trump did not want to help Ukraine stemmed from his resentment of Ukrainians, whom he saw as having worked against him in 2016, and not because he wanted them to investigate Biden for his own political gain in 2020.

Another witness who appeared on Tuesday dismissed outright the idea that Ukraine interfered in the 2016 election.

“This is a Russian narrative that [Russian] President [Vladimir] Putin has promoted,” said Lt. Col. Alexander Vindman, a Ukraine expert at the National Security Council.

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That’s true. In 2017, Putin asserted that it was Ukraine, not his own country, that had infiltrated. “As we all know, during the presidential campaign in the United States, the Ukrainian government adopted a unilateral position in favor of one candidate,” said Putin during a joint press conference with Hungarian leader Viktor Orbán.

Trump has long raged against the idea that Russian interference in the 2016 election helped him in any way. But the U.S. intelligence community, a congressional investigation and the investigation by special counsel Robert Mueller have all overwhelmingly concluded that the Russian government waged an organized effort to sow discord in the U.S. in 2016, and that its efforts were aimed at helping Trump.

Vindman’s comment echoed the testimony of his former boss, Fiona Hill, who resigned from the NSC earlier this year and who is scheduled to testify before the committee on Thursday.

“It is a fiction that the Ukrainian government was launching an effort to upend our election,” Hill told the Intelligence Committee in a deposition on Oct. 14. “I’m extremely concerned that this is a rabbit hole that we’re all going to go down in between now and the 2020 election, and it will be to all of our detriment.”

Marie Yovanovitch, former U.S. ambassador to Ukraine, testifies last Friday. (Photo: Jim Lo Scalzo/EPA-EFE/Shutterstock)

Marie Yovanovitch, the former U.S. ambassador to Ukraine, who testified last Friday in an open hearing, told Republicans who asked her about Ukraine meddling that they were barking up the wrong tree. “I would remind you again that our intelligence community has determined that those who interfered in the [U.S.] election were in Russia,” Yovanovitch said.

Republicans often point to one news article in particular when talking about Ukrainian meddling in 2016. It’s a Jan. 11, 2017, investigation published in Politico by Kenneth Vogel and David Stern. Vogel was hired by the New York Times soon after that article; Stern is now a freelancer who works for the Washington Post.

The Politico article highlighted a few isolated incidents in which leading Ukrainian officials criticized Trump. It also documented the efforts of a political consultant in the U.S. who was on contract with the Democratic National Committee and who met with top Ukrainian officials at their embassy in Washington “to expose ties between Trump, top campaign aide Paul Manafort and Russia.”

The Democratic operative, Alexandra Chalupa, shared many of her findings with journalists, including with Yahoo News’ Michael Isikoff. Manafort resigned from the Trump campaign because of scrutiny over his lobbying for pro-Russian Ukrainian oligarchs. He was sentenced to four years in prison earlier this year for bank and tax fraud related to his work in Ukraine.

Last Friday, Yovanovitch testified that, despite the criticism described in the Politico article, she saw no evidence of “a plot by the Ukrainian government to work against President Trump.”

“People are critical. That does not mean that someone or a government is undermining either a campaign or interfering in elections,” Yovanovitch said.

In addition, Volker pointed out in his testimony Tuesday that “no one in the new team governing Ukraine had anything to do with anything that may have happened in 2016. They were making television shows at the time.” Indeed, Zelensky was a TV actor in Ukraine then, starring in a popular show that ran from 2015 to 2019 and is available on Netflix, “Servant of the People.”

Brittany Shepherd contributed to this article

Cover thumbnail photo: President Trump and Day 3 of the House Intelligence Committee hearing on impeachment. (Photo illustration: Yahoo News; photos: AP, Shawn Thew/EPA/Pool via Getty Images)

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