A top GOP senator on Sunday announced new actions in a Republican-led investigation into former Vice President Joe Biden and his son Hunter — less than 24 hours after the elder Biden's primary victory in South Carolina.

According to CBS News, Sen. Ron Johnson (R-WI) sent a letter to his colleagues on Sunday, saying he wanted to subpoena witnesses related to Hunter Biden's role at the Ukrainian energy company Burisma.

Johnson, chair of the Senate Homeland Security Committee, and Judiciary Committee Chair Chuck Grassley (R-IA) initially launched the investigation in November to back up Donald Trump at the height of his impeachment inquiry.

The probe is focused on a long-debunked conspiracy regarding the Bidens and the former vice president's push in 2014 to have Ukraine's previous prosecutor general, Viktor Shokin, ousted for corruption.

Trump and his allies claim Biden only wanted Shokin fired because the prosecutor was investigating Burisma, where Hunter Biden was a board member.

But ousting Shokin was in fact a U.S. goal — one backed by a number of Republican senators including Johnson himself — as Shokin was part of Ukraine's corruption problem and was slow-walking the Burisma probe.

Ukraine's new prosecutor general has also said the Bidens did nothing wrong.

Trump was impeached in December over his efforts to force Ukraine to investigate Biden. Multiple officials testified under oath in the related inquiry that Trump withheld crucial aid and dangled the possibility of a White House visit to pressure Ukrainian leaders to announce a probe into Biden.

Democrats argued that Trump had abused the office of the presidency for personal political gain in seeking those investigations. They said Trump believed Biden would be a tough opponent in his reelection bid and that an investigation could hurt Biden's quest for the Democratic nomination.

Johnson's sudden announcement of more actions on his Biden probe has naturally drawn scrutiny, given its timing.

Biden handily won South Carolina's Democratic primary on Saturday, garnering a whopping 48.4% of the vote there, with Vermont Sen. Bernie Sanders coming in a distant second, at 19.9 percent.

Current national polling also shows that, if the election were held today, Biden would have the biggest lead over Trump, with a RealClearPolitics aggregate showing Biden would beat Trump nationally by 5.4 percent. Sen. Bernie Sanders (I-VT) has a slightly smaller edge over Trump according to RealClearPolitics, with an average 4.9 percent advantage.

In a curious twist, as Washington Post senior political reporter Aaron Blake noted Monday, "Republican members of Congress haven't sent one tweet or press release mentioning Burisma or Hunter Biden since Feb. 7, per [congressional aggregation site] Legistorm."

Johnson's announcement on Sunday was likely the first mention of the former vice president since then.

In his letter to colleagues on Sunday, Johnson announced his desire to issue subpoenas as part of his own investigation into Biden and tried to fend off criticism by saying that the investigation is "intended to discover and prevent disinformation, not advance it."

"Gathering all of the relevant information is necessary to determine not only whether any wrongdoing occurred, but also if wrongdoing did not occur," Johnson, the chair of the Senate Committee on Homeland Security, said in his letter to his colleagues.

Johnson himself was notably caught up in the Ukraine scandal in October, according to a Post report published that month.

That report revealed that Johnson had met with former Ukrainian diplomat Andrii Telizhenko in July 2019 to discuss, according to Telizhenko, the "DNC issue" — an apparent reference to another investigation Trump wanted Ukraine to open, based on a long-debunked conspiracy theory.

"I was in Washington, and Sen. Johnson found out I was in D.C., and staff called me and wanted to do a meeting with me. So I reached out back and said, 'Sure, I'll come down the Hill and talk to you,'" Telizhenko told the Post.

Published with permission of The American Independent Foundation.