US Democrats push to hear from former Trump aide Bolton in impeachment probe

ROADBLOCKS

Amid the legal roadblocks thrown up by the White House, Monday's scheduled witness, former deputy national security adviser Charles Kupperman, could fail to show up. Kupperman's lawyer says lawmakers should wait for a court to rule whether he should comply with a congressional subpoena or honor the Trump administration's order not to testify.

The Democratic-led House committees are focusing on Trump's July request to Ukrainian President Volodymyr Zelenskiy that he investigate former U.S. Vice President Joe Biden, a leading 2020 Democratic presidential candidate, and his son Hunter Biden, who had served on the board of a Ukrainian gas company.

U.S. law prohibits candidates from accepting foreign help in an election.

Acting U.S. Ambassador to Ukraine William Taylor testified last week that Trump withheld $391 million in security assistance to Ukraine in an effort to get Zelenskiy to publicly commit to investigate both the Bidens and a debunked conspiracy theory that Ukraine - not Russia - meddled in the U.S. 2016 presidential election.

Lawmakers also hope to hear from Alexander Vindman, the White House National Security Council's top Ukraine expert, on Tuesday. On Wednesday, they have lined up Kathryn Wheelbarger, the acting assistant secretary of defense for international security, and two State Department Ukraine specialists - Catherine Croft and Christopher Anderson.

Tim Morrison, a top White House adviser on Russia and Europe, is scheduled for Thursday.