President Donald Trump ignored talking points from his national security staff to address "corruption" in his phone calls with Ukraine President Volodymyr Zelenskiy, a top White House expert on Ukraine testified Tuesday in the House impeachment hearings.

Trump had phone conversations with Zelenskiy on April 21 and July 25. In memos of the calls later released by the Trump administration, the word "corruption" never came up.

Instead, Trump asked Zelenskiy in the second call to "look into" unsubstantiated allegations against former Vice President Joe Biden and his son Hunter, and to "do us a favor though" and investigate a debunked conspiracy theory alleging Ukrainian interference in the 2016 U.S. election. That call spurred Democrats to launch an impeachment inquiry into whether Trump abused his power by pressuring a foreign leader to announce investigations that would help his reelection.

Trump has argued that his interest in requesting such probes has only been to expose corruption. But Lt. Col. Alexander Vindman, a National Security Council official, testified that the official policy-based talking points provided to Trump covered the broader issue of corruption in Ukraine, not political investigations.

"Those were the recommended talking points that were cleared through the staff for the president, yes," Vindman testified.

Vindman, who listened to Trump's now-infamous July call with Zelenskiy, suggested that the talking points for that second conversation also included "anti-corruption efforts" in accordance with U.S. policy.

"The president could choose to use the talking points or not. He's the president. But they [his comments] were not consistent with what I provided," Vindman said.

Vindman added that he knows of no credible evidence to support the so-called CrowdStrike conspiracy theory, and that he is "well aware" that the theory of Ukrainian meddling has been promoted by Russian leader Vladimir Putin. U.S. intelligence officials have concluded that Russia, not Ukraine, interfered in the 2016 election with a bias toward Trump and against his Democratic rival Hillary Clinton.

Vindman testified alongside Jennifer Williams, an aide to Vice President Mike Pence, who had referred to Trump's second call with Zelenskiy as "unusual and inappropriate."