Former US president Donald Trump lashed out at Republican senate leader Mitch McConnell in a lengthy statement released on Tuesday night.
Mr Trump also vowed to provide support in electoral races for challengers to lawmakers who have crossed him, signalling his intention to further the rifts in an already divided Republican Party.
"The Republican Party can never again be respected or strong with political 'leaders' like Sen Mitch McConnell at its helm," Mr Trump said in the statement.
“Mitch is a dour, sullen, and unsmiling political hack, and if Republican Senators are going to stay with him, they will not win again,” Mr Trump wrote.
He blamed Mr McConnell for the Republicans losing their majority in the senate during the 2020 presidential elections.
“He will never do what needs to be done, or what is right for our Country. Where necessary and appropriate, I will back primary rivals who espouse Making America Great Again and our policy of America First,” Mr Trump said.
The attack came after Mr McConnell said on Saturday that even though he had voted to acquit Mr Trump at his impeachment trial, the former president was nevertheless "practically and morally responsible" for the January 6 storming of the US Capitol.
After 50 Democratic senators and seven Republicans voted that Mr Trump was guilty – a majority in the 100-seat Senate, but not the two-thirds needed for a conviction – Mr McConnell let loose, excoriating Mr Trump for the attack that saw five people die and the halls of the US legislature ransacked by Trump supporters.
He called Mr Trump's actions leading up to the siege, including a White House rally where the then-president urged followers to descend on Congress, "a disgraceful dereliction of duty."
"These criminals were carrying his banners. Hanging his flags. And screaming their loyalty to him," Mr McConnell said.
But Mr Trump blamed the veteran lawmaker, who for four years as majority leader kept the Senate aligned with the Republican president, for losing party control of the senate.
In another line of personal attack, Mr Trump took aim at Mr McConnell's wife, Taiwan-born Chinese-American Elaine Chow, who was transportation secretary in Mr Trump's cabinet but resigned in protest after the January 6 Capitol assault.
"McConnell has no credibility on China because of his family's substantial Chinese business holdings," Mr Trump wrote.
During his tenure as president, Mr Trump transformed the US Republican party, recreating it in his image. His harsh words against Mr McConnell, a longtime supporter of his, signal an attempt by Mr Trump to maintain his firm grip on the party.