The subpoena renews GOP efforts to investigate Hunter Biden’s work for Burisma, as the campaign between Mr. Biden and Mr. Trump begins to ramp up. Democrats have castigated the probe as a partisan attempt to smear Mr. Biden and have raised concerns that the investigation could dovetail with foreign disinformation efforts.

President Trump and other Republican allies have questioned Hunter Biden’s service on the board of the natural-gas company, which Ukrainian officials probed without bringing charges. Mr. Trump’s efforts to press Ukraine to open new investigations into the Bidens were at the center of his impeachment last year in the Democratic-controlled House; Mr. Trump was later acquitted in the Senate. Mr. Trump denied the Democratic charge that he had abused his power and obstructed Congress.

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