Sen. Ron Johnson, chair of the Senate Homeland Security and Governmental Affairs Committee. Photo: Samuel Corum/Getty Images

The Senate Homeland Security and Governmental Affairs Committee approved a subpoena along party lines Wednesday for documents relating to Hunter Biden and his work for Ukrainian energy company Burisma, the Washington Post reports.

Why it matters: The State Department said in 2014 that there was no conflict, noting Hunter Biden was a "private citizen." Democrats argue that the Republican-led probe is designed to damage President Trump's likely opponent Joe Biden ahead of November's election, and the committee's top Democrat,

  • Sen. Gary Peters (D-Mich.) has even suggested that the probe is aiding a Russian disinformation campaign.

Blue Star Strategies, the consulting firm that worked with Burisma while Hunter Biden was on the board, sent a letter to committee chairman Sen. Ron Johnson (R-Wis.) on Wednesday stating that they have sought to cooperate at every step and are "puzzled" by the vote to proceed with the subpoena.

  • Johnson disagreed, telling reporters that "it's way too late in the game. The only reason [Blue Star] even began talking to us again is because of the threat of subpoena."
  • Johnson said he hopes to release an interim report on the investigation before the August recess.

The backdrop: Hunter Biden began serving on the board of Burisma in 2014 and was paid as much as $50,000 per month, according to the NY Times.

  • Joe Biden was the Obama administration's point man on Ukraine, and his son's position on the board raised conflict-of-interest concerns at the time.
  • President Trump's efforts to pressure Ukraine to investigate the Bidens and Burisma culminated in his impeachment and subsequent Senate acquittal in January.

Between the lines: The president's re-election team has been planning to make Hunter Biden's work with Burisma an election-year issue by tying it to Joe Biden's vice presidency, Axios' Alayna Treene reports.

  • It comes as the Senate Judiciary Committee led by Sen. Lindsey Graham (R-S.C.) is also conducting a review of the origins of the Russia probe, another politically sensitive investigation that Graham says will be completed by October.

Go deeper: Biden promises restrictions on Hunter, family if elected

Editor's note: Moves up reference to State Department investigation.

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