(CNN) Senate Republicans are sharpening their investigations involving former Vice President Joe Biden and his son's work at a Ukrainian energy company, just as the former vice president surges in the Democratic presidential race and reemerges as the front-runner for his party's nomination.

Senate Homeland Security and Governmental Affairs Chairman Ron Johnson, a Wisconsin Republican, allowed committee members to review classified documents Wednesday evening as part of his investigation and to answer any questions they might have ahead of his plans to subpoena a consultant for a US public affairs firm that worked with Burisma, the Ukrainian energy company where Hunter Biden served as a board member. Johnson has set a vote for next Wednesday on issuing the subpoena to the consultant, who has ties to the President's personal attorney Rudy Giuliani.

Johnson told CNN Wednesday evening that he thinks there are enough votes in the committee to issue the subpoena, although at least one Republican on the panel raised concerns that the investigation could appear political.

While Republicans publicly insist their efforts have nothing to do with Biden's campaign, they are using their powers in the Senate to look into a host of matters that they believe could shine negative light on the former vice president -- and help President Donald Trump as the race heads into a crucial period. Trump and his allies have repeatedly made unfounded and false claims to allege that the Bidens acted corruptly in Ukraine.

The subpoena follows an effort from Johnson and Senate Finance Chairman Chuck Grassley, an Iowa Republican, to seek a host of records over the past several months from government agencies related to the Bidens, Burisma and Ukraine, including requests for documents to Secretary of State Mike Pompeo, Attorney General William Barr, the National Archives and the US Secret Service. Grassley has received records from the Treasury Department as part of the probe already, according to the Senate panel's top Democrat.

And Senate Judiciary Chairman Lindsey Graham is ramping up his committee's probe into the FBI's efforts to obtain a surveillance warrant under the Foreign Intelligence Surveillance Act targeting former Trump campaign adviser Carter Page, holding its first closed-door deposition on Tuesday for the investigation.

Graham, a South Carolina Republican, predicted Ukraine would be an issue during the campaign if Biden is the Democratic nominee.

"If you could run for president, and you were in charge of the Ukrainian anti-corruption campaign as vice president, and your son is sitting on the (board of the) most corrupt company in the country while you're trying to clean up the country. Yeah, that'll come up," Graham told CNN.

Asked if he would use his committee to probe the matter, Graham said: "Ron Johnson's doing it."

The Senate GOP investigations are playing out as Biden is gaining steam to become the Democratic nominee to challenge Trump in the 2020 election. The probes could become campaign fodder both to attack Biden over Ukraine and Burisma and to help the President go after the investigations into him related to Russia.

The Justice Department has also come under fire from Democrats after Barr said last month that DOJ had set up an "intake process" for the President's personal attorney to turn over Ukraine documents, even as Giuliani himself is under federal investigation.

The Senate GOP investigations into Ukraine and the Bidens are hardly the first to involve presidential politics. Democrats sharply criticized House Republicans in the runup to the 2016 presidential campaign as they investigated Hillary Clinton and the 2012 terrorist attack on the US consulate in Benghazi, which included more than 10 hours of testimony from Clinton before the House select committee. And Republicans repeatedly accused House Democrats of using their impeachment inquiry into Trump last fall as an effort to damage the President heading in the 2020 campaign.

Johnson insisted on Wednesday that his investigation wasn't about hurting Biden's 2020 bid. "My investigations are not focused on the Bidens. They just aren't," he told reporters Wednesday.

Johnson nevertheless connected his investigation to the campaign, saying the information he's seeking would be of interest to Democratic primary voters.

"We've been diligently pursuing this information, these truths, for quite some time. If things are breaking now, I can't control that. But these are questions that Joe Biden has never adequately answered. And if I were a Democratic primary voter, I'd want these questions satisfactorily answered before I cast my final vote," Johnson said.

Still, there were questions about the appearance of the investigation amid Biden's presidential surge.

Sen. Mitt Romney, who voted to convict Trump on an abuse of power charge, said he hasn't decided on whether to back a subpoena but would discuss the matter with his colleagues.

Asked if he thinks the probe may be politically motivated, the Utah Republican said: "I think at this stage, it certainly has that appearance."

Republicans hold an 8-6 advantage on the Homeland Security Committee. So if Romney breaks ranks, it could be enough to scuttle Johnson's push.

Asked about Romney's concerns, Johnson said the he hoped to allay them by meeting with members about the probe. "Committee members aren't fully involved with this like I am. That's why I want to be there and answer any question they have and ease their mind," he said.

Another Republican on the panel, Sen. Rick Scott of Florida, said Wednesday he was still reviewing the material and didn't know how he would vote on the subpoena next week.

Rand Paul, a Kentucky Republican who sits on Johnson's committee, said he informed the chairman that he will "support subpoenas to investigate" the Bidens and Burisma, saying the matter should be probed.

Biden has said the actions he took had nothing to do with his son. Multiple witnesses during the House's impeachment inquiry testified that Joe Biden's actions in Ukraine pushing for the removal of a Ukrainian prosecutor were consistent with official US government policy, backed at the time by European allies and both Republicans and Democrats in Congress, including Johnson.

Biden campaign spokesman Andrew Bates said that Johnson's comments Wednesday referencing Democratic primary voters was an admission "that he is 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. Now, Senator Johnson just flat out conceded that this is a ham-handed effort to manipulate Democratic primary voters," Bates said.

Graham said that he is focused on the FISA investigation, not Ukraine and Burisma, saying Wednesday his primary concern is that whatever comes out of Ukraine is vetted by the intelligence community. But Graham had previously joined Johnson and Grassley on a request for documents to the State Department, and he said Wednesday he is still interested in "how did (State) miss the conflict" when they were told Hunter Biden served on the board of Burisma while Joe Biden was leading the administration's Ukraine policy.

Subpoena vote next week

Johnson said his committee would hold a business meeting on Wednesday next week to consider a subpoena for records to Andrii Telizhenko, the former consultant for Blue Star Strategies, who indicated he wants to cooperate in the probe but needs a subpoena to provide the documents he has. The committee has to take up the subpoena for a vote because Sen. Gary Peters of Michigan, the top Democrat on the panel, opposed Johnson's request to subpoena Telizhenko last month.

Peters did not say whether he thought the committee's investigation was an effort to harm Joe Biden, but he argued there were better things for the committee to be focusing on.

"This investigation should not be part of what we're doing in Homeland Security," Peters said. "Let's focus on the work at hand, which is protecting the homeland against Coronavirus and cyberattacks and the entire list of threats that we face as a country."

Johnson's investigation is probing allegations surrounding Hunter Biden's work for Burisma while Joe Biden pushed for the firing of Ukrainian prosecutor general Viktor Shokin, which was US policy at the time. The allegations were featured prominently in the impeachment defense of the President. Hunter Biden told ABC News last year that it was "poor judgment" for him to take the job with Burisma, but he said he did nothing improper in the role.

Johnson is also looking into conspiracy theories that Ukraine meddled in the 2016 elections, which impeachment witnesses like Fiona Hill said were part of a Russian disinformation campaign to distract from Moscow's election meddling effort.

Johnson said his committee could potentially release an interim report in the next month or two detailing their findings to date in the probe.

Telizhenko is a stalwart Giuliani ally and helped spread the conspiracy theory that Ukraine meddled to defeat Trump in 2016. He claims that he witnessed some of the anti-Trump efforts while working as a junior diplomat at the Ukrainian embassy in Washington, but top Ukrainian officials have denied these claims and said Telizhenko is not credible. Last year, Telizhenko participated in meetings between Giuliani and two disgraced Ukrainian prosecutors who accused the Bidens of corruption.

Virginia Sen. Mark Warner, the top Democrat on the Senate Intelligence Committee, said there was bipartisan agreement that evidence shows Russian intelligence sought "to promote this absurd theory of Ukraine involvement in prior elections." He warned senators not to allow their investigation to be used to bolster Russian propaganda about Ukraine.

"I hope my colleagues are not knowingly becoming tools of Russian propaganda and the Russian (intelligence) services efforts to sow chaos in our country," Warner said.

This story has been updated with additional developments Wednesday.