“It is not only appropriate, but it is our duty to investigate if we think there was interference in the election of 2016,” Mr. Pompeo said in Athens. “I think everyone recognizes that governments have an obligation — indeed, a duty — to ensure that elections happen with integrity, without interference from any government, whether that’s the Ukrainian government or any other. And so inquiries with respect to that are completely important.”

He added: “There’s been some suggestion somehow that it would be inappropriate for the United States government to engage in that activity, and I see it just precisely the opposite. I see our duty to engage in activity that ensures that we have fair, free elections.”

A White House reconstruction of the July 25 call, which Mr. Pompeo listened to as the conversation unfolded, showed that Mr. Trump asked Mr. Zelensky to “do us a favor” and investigate whether people in Ukraine were involved in the stealing of emails from the Democratic National Committee during the 2016 presidential campaign.

[Read: Ukraine’s Zelensky was ready to bow to Trump’s demands, but was spared by luck.]

Rudolph W. Giuliani, the president’s personal lawyer, is pushing an unsubstantiated conspiracy theory that the Ukrainians framed the Russian government by making it look like a Ukrainian hack of the Democratic committee was the work of Moscow.

In fact, American intelligence officials and prosecutors have cited ample evidence that it was Russia that stole the emails to embarrass Hillary Clinton, Mr. Trump’s Democratic challenger in 2016.