A day after threatening to withhold his vote, Sen. Mitt Romney signaled Friday that he will support a Republican effort to obtain documents and testimony relating to work done in Ukraine by the son of former vice president Joe Biden.

Romney (R-Utah) will vote for issuing a subpoena in the Senate Homeland Security and Governmental Affairs Committee next week after receiving assurances from the panel’s chairman, Sen. Ron Johnson (R-Wis.), “that any interview of the witness would occur in a closed setting without a hearing or public spectacle,” Romney spokeswoman Liz Johnson said in a statement.

“He will therefore vote to let the chairman proceed to obtain the documents that have been offered,” the statement said.

Romney joined Democrats last month in voting to convict President Trump of abuse of power based on his dealings with Ukraine; the president was acquitted on the impeachment counts. On Thursday, Romney said Sen. Johnson’s probe had the appearance of being politically motivated to target Trump’s potential general-election rival.

“I would prefer that investigations are done by an independent, nonpolitical body,” he said.

The subpoena vote, set for Wednesday, comes as Trump and his Republican allies refocus their attention on Biden’s connections to Ukraine after his sudden surge in the race for the Democratic presidential nomination. Trump said in a Fox News Channel interview Wednesday that he planned to make those connections a “major issue” in the presidential race should Biden win the nomination.

“I will bring that up all the time,” he told host Sean Hannity.

The key circumstance surrounds the service of Biden’s son Hunter Biden on the board of Burisma, a Ukrainian energy company — a sinecure that paid him hundreds of thousands of dollars at a time when Joe Biden was engaged in diplomacy in Ukraine as vice president on behalf of the Obama administration.

Trump and his allies have alleged, with no direct evidence, that Biden corruptly pushed to remove Ukraine’s chief prosecutor to protect his son’s financial interests. In fact, Biden moved to remove the prosecutor, Viktor Shokin, in concert with Obama administration policy and the anti-corruption efforts of multiple U.S. allies.

In a 2016 letter to then-Ukrainian President Petro Poroshenko, Johnson joined Republican and Democratic senators in seeking changes to the prosecutor’s office similar to what Biden had sought.

In the Senate investigation, Johnson has pushed for more information on Hunter Biden’s activities — requesting, for instance, Secret Service records last month pertaining to Hunter’s travel during his father’s vice presidency.

The subpoena Johnson is pursuing seeks documents and testimony from Andrii Telizhenko, a former Ukrainian diplomat who worked for Blue Star Holdings, a firm that represented Burisma in the United States. The top Democrat on the Homeland Security Committee, Sen. Gary Peters of Michigan, objected to the subpoena last month, forcing the vote.

“Quite frankly, the Homeland Security Committee should be focusing on issues related to homeland security,” Peters said Thursday.

Democrats and some Republicans have warned that Russia has sought to plant disinformation to amplify the Biden-Ukraine allegations and sow discord ahead of the November election. Peters on Friday called on Johnson to arrange a classified briefing for the panel’s members to address those concerns.

“This is a matter of national security, and our Committee members must have the opportunity to get classified updates from our law enforcement and intelligence community experts to prevent the Committee from being used to advance information that could benefit foreign adversaries and undermine the integrity of our elections,” Peters wrote.

With every Democrat expected to oppose the measure, Romney’s opposition could have blocked the issuance of the subpoena.

Another Republican on the committee, Sen. Rob Portman of Ohio, said Thursday that he was undecided on authorizing the subpoena. On Friday, he told reporters in Cleveland that he wanted to learn more about the subpoena but was “inclined to support the chairman on getting more information.”

“I just want to understand it better, just what the information is likely to be and why it’s important,” Portman said, according to a transcript provided by his office.

Johnson said Thursday that he hopes to put out a report in the coming months — amid the thick of the presidential campaign — that details what is known and what is unknown about Ukrainian entanglements in U.S. politics, including with the Bidens.

He denied any political motivations. “It’s about getting information,” he said. “Congressional oversight is all about informing, for example, public policy, but also informing the public.”

In an interview Thursday night on Fox News, Senate Majority Leader Mitch McConnell (R-Ky.) signaled his support for Johnson’s effort.

“I think it’s worth taking a look at,” McConnell said.