Lawmakers attending closed-door interviews say testimony from State Department officials and those in other foreign policy posts is largely corroborating the account of the government whistleblower whose complaint sparked the probe.
House Speaker Nancy Pelosi appears not to be willing to give in to Republican demands for a formal vote on the impeachment inquiry.
Pelosi told reporters Tuesday that the investigation is raising new questions about Trump's relationship with Russia's president, Vladimir Putin. She says that with Trump, "all roads seem to lead to Putin."
Trump calls the impeachment inquiry an "illegitimate process."
Scheduled to appear on Wednesday is a former top aide to Secretary of State Mike Pompeo, Michael McKinley.
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