WASHINGTON — Republicans are wielding the power of their Senate majority to intensify an election-year investigation of Hunter Biden’s work for a Ukrainian energy firm, putting new scrutiny on the son of Joseph R. Biden Jr. as the former vice president re-emerges as President Trump’s chief rival for the presidency.
In elevating questions about the younger Mr. Biden’s work in Ukraine, Senate Republicans are effectively picking up where the president left off last year when he pressed the country’s leaders to investigate the Bidens, an effort that led to his impeachment in the House on charges that he abused his power by seeking foreign help in the 2020 election. It is part of a broader attempt by his allies on Capitol Hill to breathe fresh life into politically charged inquiries into issues that have preoccupied Mr. Trump.
Senator Ron Johnson, Republican of Wisconsin and the chairman of the Homeland Security Committee, plans to hold a vote next week despite Democratic objections to issue a rare Senate subpoena to Andrii Telizhenko, a former Ukrainian official who worked for Burisma, the energy firm. Mr. Johnson told reporters on Wednesday that he would release an interim report this spring summarizing what Republicans had learned from months of quiet queries.
For now, Republicans insist Burisma is a matter of longstanding interest unrelated to Mr. Biden’s presidential candidacy, and no evidence has emerged to suggest that either Biden acted improperly. But Mr. Johnson acknowledged that his investigation could affect the election and said that was as it should be.
“These are questions that Joe Biden has never adequately answered,” Mr. Johnson told reporters in the Capitol, a day after Mr. Biden’s remarkable Super Tuesday turnabout. “And if I were a Democrat primary voter, I’d want these questions satisfactorily answered before I cast my final vote.”
The increased interest in the Bidens comes as Senate Republicans have ramped up other investigations that could benefit Mr. Trump politically, including an inquiry into the F.B.I.’s Russia investigation and claims that Democrats colluded with Ukraine in the 2016 election.
Mr. Biden’s campaign has branded the Johnson investigation an abuse of congressional authority and maintained that it would find no evidence of wrongdoing by the former vice president or his family. But Democrats are concerned that Republicans are trying to recreate their playbook for the run-up to the 2016 election, when Mr. Trump — aided by Republicans and Fox News — worked to weaponize a steady stream of small disclosures from an investigation into Hillary Clinton to cast her as secretive and potentially corrupt.
Some Republicans have privately voiced discomfort about the effort. On Thursday, Senator Mitt Romney, Republican of Utah and a member of the Homeland Security Committee, told reporters that there was “no question” that “looking into Burisma and Hunter appears political.” He said he was not yet sure if he would support the subpoena.
Mr. Romney was the only member of his party who voted at the Senate impeachment trial to convict Mr. Trump of abuse of power and remove him from office.
“People are tired of these kind of political investigations, and would hope that if there is something of significance that needs to be evaluated, it would be done by perhaps the F.B.I. and some other agency that is not as political as a committee of our body,” he said.
But Mr. Trump has embraced the effort, using his megaphone to try to create a shroud of innuendo and doubt about an increasingly viable opponent. On Wednesday, he circulated on Twitter a report about Mr. Johnson’s investigation and later told Sean Hannity of Fox News that portraying the Bidens as corrupt would be a central theme of his bid for re-election.
“That will be a major issue in the campaign,” Mr. Trump said in the interview. “I will bring that up all the time.”
At issue is Hunter Biden’s position on the board of Burisma, a Ukrainian oil and gas company with a history of corruption, which he held while his father served as vice president overseeing United States policy toward the former Soviet republic. The younger Mr. Biden had no expertise on energy issues and was paid a large salary. Mr. Trump and Republicans have continually raised questions about the arrangement, claiming with no evidence that it was part of a corrupt scheme.
Mr. Johnson and Senate Republicans are specifically investigating whether Burisma used Hunter Biden’s name and influence to gain access to the Obama administration.
The investigation closely resembles the one that Mr. Trump pressed Ukraine to undertake last year into whether Mr. Biden sought to remove a Ukrainian prosecutor for investigating Burisma. That allegation has been discredited — the prosecutor, Viktor Shokin, was widely viewed as corrupt, and his removal was supported by many American and European officials. (Mr. Johnson was among the Republican and Democratic senators who signed a letter at the time calling for “urgent reforms” to his office.)
But Republicans mounting an impeachment defense for the president in the Senate later said Mr. Trump had been justified in wanting Ukraine to scrutinize the episode, insisting that the president had been asking for a legitimate investigation of possible corruption, not a political favor to smear a rival.
Now, Republican senators argue that Mr. Biden’s son is fair game.
“I am not saying Joe Biden is corrupt — far from it,” said Senator Lindsey Graham of South Carolina, the chairman of the Judiciary Committee. “But he had knowledge that his son was sitting on the most corrupt board in the Ukraine, when he was trying to clean up the Ukraine. We are going to hold him accountable for that.”
Democrats say Senate Republicans are knowingly raising a false flag for an operation designed to legitimize claims by Mr. Trump and some in the conservative news media.
“What is actually new here?” said Senator Ron Wyden of Oregon, one of the Democrats trying to counter the inquiry. “There is no evidence to date that has implicated Vice President Biden in wrongdoing of any kind, and we base that on our review of hundreds of documents.”
Andrew Bates, a spokesman for Mr. Biden’s campaign, accused Mr. Johnson of “abusing congressional authority in a manner that would make the founding fathers spin in their graves.”
“We already knew that Donald Trump is terrified of facing Joe Biden — because he got himself impeached by trying to force a foreign country to spread lies about the vice president on behalf of his re-election campaign,” Mr. Bates said. “Now, Senator Johnson just flat-out conceded that this is a ham-handed effort to manipulate Democratic primary voters.”
Those leading the inquiries insist their focus on Burisma is not politically driven, noting that it dates to 2017, before it was clear that Mr. Biden would be a presidential candidate.
“We are proceeding with the investigation whether Biden is in or out,” said Senator Charles E. Grassley, Republican of Iowa and the chairman of the Finance Committee, who co-signed numerous requests with Mr. Johnson. “This investigation is about conflicts of interest, not political candidates.”
In addition to the Burisma matter, Mr. Johnson and Mr. Grassley are investigating whether Democrats conspired with Ukrainian officials to harm Mr. Trump’s campaign in 2016. Senator Richard Burr, Republican of North Carolina and the chairman of the Intelligence Committee, has previously warned his fellow chairmen in private that any investigation that turned on information from Ukraine should be handled delicately because it could advance Russian efforts to spread disinformation, according to two officials familiar with the discussions, which were first reported by Politico. (Mr. Burr said this week that he had no objection to Mr. Johnson’s investigation.)
It is unclear how far the Burisma investigation has advanced. The senators indicated they had received documents from multiple individuals in recent weeks, and the State Department has handed over 2,800 pages of records.
Mr. Johnson sought approval for the subpoena from Senator Gary Peters of Michigan, the top Democrat in the Homeland Security Committee, but Mr. Peters refused, citing concerns similar to Mr. Burr’s.
In a letter to committee members on Sunday informing them of the subpoena vote next week, Mr. Johnson stressed that his staff was going to “great lengths” to consult with intelligence and law enforcement officials first.
“I share the ranking member’s interest in ensuring that the Senate and this committee not be used to advance disinformation,” he wrote in the letter, which came the day after Mr. Biden won the South Carolina primary.