According to the whistle-blower complaint accusing Mr. Trump of improperly pressuring Ukraine on those subjects, Mr. Pence planned to attend the May inauguration of Ukraine’s new president, Volodymyr Zelensky, but canceled his trip at the instruction of Mr. Trump, who was seeking to pressure the Ukrainian government to investigate the Bidens. But a source in Mr. Pence’s office said that no such trip had been planned.

And when Hurricane Dorian led Mr. Trump to cancel an early-September trip to Warsaw on which he was set to meet with Mr. Zelensky, Mr. Pence traveled in place of the president. While there, on Sept. 2, Mr. Pence denied to reporters that he had discussed the elder Mr. Biden with the Ukrainian leader.

“The president asked me to meet with President Zelensky and to talk about the progress that he’s making on a broad range of areas,” Mr. Pence said. “And we did that.”

Mr. Pence did not directly respond to a question at the time about whether the Trump administration had held up $391 million in military aid for the country this summer in order to further pressure Mr. Zelensky’s government. Instead he cited Mr. Trump’s complaint that Europe has not done more to assist Ukraine, adding that “as President Trump had me make clear, we have great concerns about issues of corruption.”

By that time, Mr. Trump’s public remarks had already conflated well-established concerns about endemic corruption in Ukrainian society with his more personalized notion of corruption in the country — namely the alleged activities of the Bidens and unfounded theories that it was Ukraine’s government that meddled in the 2016 election, not Russia’s.

Mr. Pence’s critics say that despite the vice president’s professions of ignorance about the core of Mr. Trump’s political agenda in Ukraine, he knew enough about the president’s mixing of foreign policy and politics to be implicated in any wrongdoing.

At the same time, Mr. Pence appears to have been almost willfully oblivious to Mr. Trump’s public obsession with Ukraine, the Bidens and conspiracy theories surrounding the 2016 election that have also been amplified in public by Mr. Trump’s lawyer, Rudolph W. Giuliani.