The Biden clan still needs to explain why a vice president’s son was enjoying a $50,000-per-month gig for which his principal qualification appears to have been his last name. But Joe Biden isn’t the only pillar of the Democratic establishment who won’t enjoy the new spotlight on American relations with Ukraine. And President Donald Trump isn’t the only one who wants a fuller accounting of that country’s role in the 2016 U.S. presidential election.

In a letter released on Monday morning, Republican senators Chuck Grassley...