The former Senate Majority leader slammed Mr Trump for his potential criminal conduct just moments after he was acquitted 57-43 in his historic second impeachment trial on Saturday.
Now Mr Trump has had his revenge in a cutting statement released on Tuesday – his most significant statement since leaving office on 20 January – urging lawmakers to dump the veteran Kentucky politician.
“Mitch is a dour, sullen, and unsmiling political hack, and if Republican Senators are going to stay with him, they will not win again. He will never do what needs to be done, or what is right for our country,” said Mr Trump.
The former president said that the GOP would “never again be respected or strong” with Mr McConnell “at its helm”.
“McConnell’s dedication to business as usual, status quo policies, together with his lack of political insight, wisdom, skill, and personality, has rapidly driven him from Majority Leader to Minority Leader, and it will only get worse,” he added.
Watch: Lindsey Graham says Mitch McConnell was 'indispensable to Trump’s success'
Mr Trump also attacked Mr McConnell over China. The senator is married to the ex-president’s former secretary of transportation Elaine Chao, who was born in Taiwan. She resigned from her post after Mr Trump’s supporters launched a lethal insurrection at the US Capitol on 6 January.
“McConnell has no credibility on China because of his family’s substantial Chinese business holdings. He does nothing on this tremendous economic and military threat,” he said.
Mr Trump said that he is willing to back anyone in primary battles against sitting Republicans, “who espouse Making America Great Again and our policy of America First.”
And he added: “We want brilliant, strong, thoughtful and compassionate leadership.”
“This is a big moment for our country, and we cannot let it pass by using third rate ‘leaders’ to dictate our future!”
Mr McConnell spoke out against Mr Trump, despite voting not to convict him at trial, and firmly blamed him for the violence that his supporters unleashed at the Capitol on 6 January.
“They did this because they had been fed wild falsehoods by the most powerful man on earth because he was angry he had lost an election,” said Mr McConnell at its conclusion.
“Former president Trump’s actions that preceded the riot were a disgraceful, disgraceful dereliction of duty.”
Mr Trump received 57 votes to convict him in the Senate impeachment trial, but it did not meet the two-thirds mark of 67 votes.
The seven GOP senators who voted to convict Trump were Richard Burr of North Carolina, Bill Cassidy of Louisiana, Susan Collins of Maine, Lisa Murkowski of Alaska, Mitt Romney of Utah, Ben Sasse of Nebraska and Pat Toomey of Pennsylvania.
All have faced a fierce backlash from party members.
Mr Trump is the first president in US history to be impeached by the House twice, and the first to be tried for impeachment after leaving the White House.
In not convicting him, the Senate allowed Mr Trump, 74, to run again for president in 2024.
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