Sen. Elizabeth Warren (D-Mass.) released a new ethics plan last week, focused on ending corruption in Washington and banning private lobbying of foreign governments, among other things.

Warren, who happens to be gaining ground on former Vice President Joe Biden in Democratic primary polls, was asked Wednesday if her plan would allow the child of a vice president to be appointed to the board of a foreign corporation — a clear reference to Hunter Biden's business in Ukraine while Biden was vice president.

The senator did not seem prepared for that question and noticeably stumbled over her inconclusive response.

"No. I don't — I don't know," Warren said. "I mean, I'd have to go back and look at the details on the plan."

It was an unflattering moment for a top-tier candidate who has built her reputation and credibility on plans and policy knowledge. It's unclear whether Warren hesitated because she truly didn't know the answer, or whether she was trying to avoid admitting that Biden's son had unethically leveraged his father's position for financial gain overseas.

Warren has avoided directly attacking other Democratic primary candidates, even Biden, who she has been trailing in every poll until recently.

Democrats are also likely to avoid drawing attention to Biden's Ukraine controversy as they try to impeach President Donald Trump over an alleged "quid pro quo" arrangement with Ukraine President Volodymyr Zelensky, in which Democrats claim Trump tried to leverage foreign aid money to pressure Ukraine to investigate Hunter Biden.

A transcript of a July phone call between the two leaders confirmed that the president indeed asked Zelensky to investigate the Bidens, but he did not say or strongly imply that their failure to do so would have resulted in the withholding of aid.

President Trump did delay the release of the aid to Ukraine a week before the call, eventually releasing it on Sept. 11. Trump has said he delayed it over corruption concerns, and because he felt European countries should be doing more to support Ukraine.

(H/T: Washington Free Beacon)