WASHINGTON — Lt. Col. Alexander Vindman, the National Security Council staffer set to deliver dramatic testimony confirming that President Donald Trump sought dirt on a political rival from Ukraine, is a Jewish refugee from that country when it was part of the Soviet Union.“I did not think it was proper to demand that a foreign government investigate a U.S. citizen, and I was worried about the implications for the U.S. government’s support of Ukraine,” Vindman, an army officer and the top NSC official handling Ukraine, says in testimony posted Monday evening by the New York Times, which he is set to deliver to congressional investigators on Tuesday.Trump has denied that he sought a quid pro quo in a July phone call with the Ukraine president, Volodymyr Zelensky, in which he asked the Ukrainian to investigate former Vice President Joe Biden, a leading contender for the Democratic presidential nomination. Trump simultaneously was withholding close to $400 million in congressionally approved defense assistance to Ukraine. Trump released the assistance last month, and has insisted that it was not withheld as a means of pressuring Ukraine to seek dirt on the Bidens.Vindman, who listened in on the conversation in his official capacity, would be the first whistleblower to have first-hand knowledge of the call.“I realized that if Ukraine pursued an investigation into the Bidens and Burisma it would likely be interpreted as a partisan play which would undoubtedly result in Ukraine losing the bipartisan support it has thus far maintained,” he said in his prepared testimony. Burisma is a mining concern that for a period employed Biden’s son, Hunter. Allegations by Trump and others that Biden and his son were engaged in corrupt behavior have not been substantiated.Vindman earned a purple heart when he was wounded in Iraq.An online album by Carol Kitman, a photographer, documents the life of Vindman and his twin brother Eugene, who also served in the military, since she spotted them in 1980, then 4 years old, strolling in Brighton Beach in New York City, with their grandmother. They had arrived from the Soviet Union in 1979, according to Kitman.Kitman used the boys as models in a Jewish counting book, “One Mezuzah.” One of the online album photos shows them learning Torah from a rabbi, the husband of her coauthor.Another photo shows Alexander marrying his wife, Rachel, under a tallit. Eugene is a lawyer on the national security council.