Speaker of the House Kevin McCarthy has opened the door – at least a crack – on starting impeachment proceedings against President Joe Biden.

In comments made during a Fox News interview, the California Republican said that congressional investigations into Mr Biden’s possible ties to the financial dealings of his son, Hunter Biden, are “rising to the level of an impeachment inquiry”.

Impeachment by the House of Representatives it the first step in a formal process to remove a president – or other senior executive or judicial official – from office. It requires a simple majority vote in the chamber to trigger a trial in the US Senate, where a two-thirds majority is necessary for conviction and removal.

President Donald Trump was impeached twice when Democrats controlled the House – over Ukraine in 2019 and the January 6 Capitol riot in 2021 – but was acquitted by the Senate on both occasions.

Mr McCarthy has not mentioned specific charges, but Republicans are running a series of investigations.

The speaker’s comments on Monday come the week after a House committee heard testimony from two Internal Revenue Service officials who claimed Mr Biden’s Justice Department prevented a more thorough investigation of the president’s involvement in Hunter Biden’s personal finances.

Last Thursday, Republican Senator Chuck Grassley released a Federal Bureau of Investigation document detailing how a trusted intelligence source had passed along allegations that the Biden family had received two $5 million payments from a Ukrainian energy company after then Vice-President Biden pressured Ukraine to remove a senior government official in charge of investigating corruption.

Next week, a former Hunter Biden business associate will testify privately to a House Committee that Joe Biden was more involved in his son’s business dealings than the president has acknowledged.

Neither the IRS investigators nor the FBI document provided conclusive evidence of illegal or improper conduct by the president, but Republicans in the House have asserted that the information should be enough to trigger a formal impeachment inquiry.

Mr McCarthy, in his comments to Fox, went on to say that impeachment proceedings would give House Republicans powerful new tools to investigate allegations of Biden financial impropriety and “get the rest of the knowledge and information that’s needed”. He went on to draw parallels with the administration of Richard Nixon, who was the target of a congressional inquiry in 1974 but resigned before he was formally impeached.

“We’re watching this administration use government much like Richard Nixon by denying us to get the information that we need,” he said.

In the past, the House speaker had been reluctant to endorse calls from some Republicans in his chamber to initiate impeachment proceedings, saying that it was too soon to follow that course of action.

And at a closed-door meeting with House Republicans on Wednesday, Mr McCarthy reportedly tempered his earlier comments, saying his party would only launch a formal investigation when the evidence supported it.

The ultimate success of an impeachment resolution in the House is very much in doubt. Republicans hold a narrow majority in the chamber and some centrists in the party, contemplating challenging re-election races in November 2024, have expressed unease with moving forward with a process that will only enflame political divisions in America.

The Biden team was quick to push back against Mr McCarthy’s comments.

“Instead of focusing on the real issues Americans want us to address like continuing to lower inflation or create jobs, this is what the House GOP wants to prioritise,” wrote White House spokesman Ian Sams in a social media statement. “Their eagerness to go after [Mr Biden] regardless of the truth is seemingly bottomless.”

Only three US presidents have been impeached – Andrew Johnson in 1868, Bill Clinton in 1998 and Donald Trump twice. None was convicted by the Senate.

Democrats currently have a 51-49 majority in the Senate, virtually ensuring that any Biden impeachment referral from the House will meet a similar fate.