Sen. Mitt Romney is backing a new Senate probe involving Vice President Joe Biden and his son Hunter that could be a thorn in the side of the former vice president as he campaigns for the White House.

Romney had expressed reservations on whether to join with the rest of the Republicans on the Senate Homeland Security Committee on an expected vote next week to subpoena documents over concerns the investigation may appear politically driven.

But after assurances from the committee chairman, Sen. Ron Johnson, R-Wis., Romney won't thwart the effort, his spokesperson said Friday.

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“Senator Romney has expressed his concerns to Chairman Johnson, who has confirmed that any interview of the witness would occur in a closed setting without a hearing or public spectacle," said Liz Johnson, Romney's communications director. "He will therefore vote to let the Chairman proceed to obtain the documents that have been offered.”

Republicans only have an 8-6 majority on the committee, so Romney was critical because a 7-7 tie would result in the vote failing. The Utah senator was already in hot water with President Trump's base for being the only Republican to vote in favor of impeaching the president for seeking an investigation by Ukraine into the Bidens that could muddy up the 2020 presidential election.

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The GOP-led committee is expected to vote next Wednesday on a subpoena seeking records of Blue Star Strategies' former consultant Andrii Telizhenko.

Blue Star was contracted with Bursima Holdings, a Ukrainian gas company, while Hunter Biden sat on its board and Joe Biden was the Obama administration's point person on Ukraine policy. The State Department in the Obama administration considered Burisma to be a corrupt company, a categorization that Blue Star was attempting to change, allegedly leaning on the fact that the younger Biden was on its board.

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Telizhenko has told the committee he is willing to cooperate with it, but he has a nondisclosure agreement with Blue Star that he cannot break unless he is subpoenaed. The committee is seeking more clarity as to what exactly Blue Star's objective was in regard to the State Department.

Democrats have said that various Senate investigations related to the Biden family are not actually good-faith investigations into potential wrongdoing, but political efforts to boost Trump's reelection chances.

Trump was acquitted on two articles of impeachment -- abuse of power and obstruction of Congress -- for withholding security aid to Ukraine while asking the new president to investigate the Bidens.

After Trump's acquittal, GOP leaders in the Senate said they want to take up the investigation that Trump had requested into potential corruption by the Bidens in Ukraine. The Bidens have denied any wrongdoing and Joe Biden says the efforts against him and his family are a sign of how worried Trump is about potentially facing him in November on the ballot.

Fox News' Edmund DeMarche and Tyler Olson contributed to this report.