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It’s the one question about impeachment that no Democratic presidential candidate wants to answer head on.

Should Joe Biden’s son Hunter have been allowed to sit on the board of a foreign company while his father served as vice president?

In the past few weeks, Mr. Biden and his campaign team have spent significant amounts of time and energy denouncing any whiff of impropriety between his son’s work and his service as vice president.

They’re right: There is no evidence that Hunter Biden made millions of dollars from his overseas work or that his father intervened inappropriately with Ukraine or China on his behalf, as President Trump has falsely claimed.