Former 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."
His statement came after Mr McConnell said the former president was "morally responsible" for the US Capitol riots.
The exchange exposed an apparent rift between the two over the future of the Republican party.
The majority of Republican senators backed Mr Trump in his impeachment trial last week, including Mr McConnell who voted to acquit.
But in a speech on the Senate floor, Mr McConnell implied the former president should face criminal and civil litigation because he was "still liable for everything he did while in office".
He said Mr Trump's actions prior to the riots on 6 January amounted to "a disgraceful dereliction of duty".
The feud has prompted concern among some Republicans about the impact it may have on next year's mid-term elections. The party is trying to regroup having lost the House, the Senate and the presidency.
"I'm more worried about 2022 than I've ever been," Senator Lindsey Graham told Fox News.
"I don't want to eat our own," he added. "We need to knock this off."
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" cost the Republicans control of the Senate following last November's elections, he said.
Two closely-contested run-off votes in Georgia saw the Republicans lose both seats to Democrats, resulting in a 50-50 split of seats in the Senate. This leaves the Democrats in control because Vice-President Kamala Harris has the casting vote in the case of a tie.
Mr Trump also 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.
Politico reported that an early draft was even more personal, with a source telling the site it said Mr McConnell had "too many chins but not enough smarts".
A telling political attack
Donald Trump's Twitter ban may mean that he has lost his favourite way of lobbing attacks at his opponents, but his latest press release about Senate Minority Leader Mitch McConnell shows he hasn't lost his bite.
There's a lot of invective in the eight-paragraph diatribe from the former president, but the line that will give the Republicans the most heartburn is toward the end, when he says he will back primary challenges against members of his own party "where necessary and appropriate".
It's telling that as Mr Trump prepares to re-enter the fray after his impeachment trial, he does so with an attack on his own party, not the Democrats.
Trump may eventually take aim at Joe Biden and the left, but the political warfare Trump appears most interested in at the moment is of the internecine variety.
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 riots, which led to the deaths of five people including a police officer.
Mr Trump, who was impeached by the House of Representatives over the violence, was acquitted by the Senate on charges of inciting the insurrection.
Only seven Republicans joined the Democrats in voting to convict Mr Trump. Mr McConnell and 42 other Republicans voted to acquit.
A two-thirds vote was needed to convict.
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," he said.
"A mob was assaulting the Capitol in his name," he added. "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," Jason Miller told 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".
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