Former US President Donald Trump has launched a scathing personal attack on fellow Republican Mitch McConnell.
"Mitch is a dour, sullen, and unsmiling political hack," said Mr Trump, "and if Republican Senators are going to stay with him, they will not win again."
Mr McConnell, who led the Senate for years, voted to acquit Mr Trump in his impeachment trial last week, reports BBC.
But he then attacked him as "morally responsible" for the US Capitol riot because of his election fraud "lies".
In a speech on the Senate floor, he implied Mr Trump should face criminal and civil litigation, because he was "still liable for everything he did while in office".
What did Trump say about McConnell?
Mr Trump responded on Tuesday with his lengthiest statement since he left office a month ago.
"The Republican Party can never again be respected or strong with political 'leaders' like Senator Mitch McConnell at its helm," the press release reads.
Mr McConnell's "lack of political insight, wisdom, skill, and personality" had cost the Republicans control of the Senate following last November's elections, he said.
The former president said the Republican leader "begged" for his endorsement in his own Senate race, without which Mr Trump claimed Mr McConnell would have lost.
Mr Trump took aim at Mr McConnell's stated intentions to stand in the way of future Trump-backed candidates.
The former president said he would back Republican primary challengers who "espouse Making America Great Again and our policy of America First".
Mr McConnell "will never do what needs to be done, or what is right for our Country," said Mr Trump.
"We know our America First agenda is a winner, not McConnell's Beltway First agenda or Biden's America Last."
When did McConnell and Trump's relationship sour?
The two Republicans shared a cordial working relationship throughout Mr Trump's presidency.
That changed, however, after Mr Trump lost the presidential election.
Mr McConnell said he had not spoken to Mr Trump since mid-December.
The rift between them was exacerbated after the Capitol riot on 6 January, which led to the deaths of five people including a Capitol police officer.
Mr Trump, who was impeached by the House of Representatives in January for inciting the insurrection, was acquitted by the Senate on Saturday.
Only seven Republicans joined the Democrats in voting to convict Trump. Mr McConnell and 42 other Republicans voted to acquit.
A two-thirds vote was needed to convict the former president.
Despite voting to acquit, Mr McConnell excoriated the former president on the Senate floor after the vote.
"There is no question, none, that President Trump is practically and morally responsible for provoking the events of the day," Mr McConnell said.
"A mob was assaulting the Capitol in his name," he said. "These criminals were carrying his banners, hanging his flags and screaming their loyalty to him."
The relationship between Mr Trump and Mr McConnell is not the only one to have soured over the past month.
On Tuesday, an adviser to Mr Trump said that former New York City mayor Rudy Giuliani has stopped doing legal work for the former president.
Mr Giuliani is "not currently representing President Trump in any legal matters," said Jason Miller on CNN.
Mr Trump reportedly tried to stop paying Mr Giuliani's legal fees in a fit of irritation about being impeached a second time, US media reported in January.
But Mr Miller clarified on Twitter after the interview that Mr Giuliani remains "an ally and a friend".
He explained that they are simply not working together because "there are no pending cases where Mayor Giuliani is representing the President".