"When the former Governor of the Great State of South Carolina, @MarkSanford, was reported missing, only to then say he was away hiking on the Appalachian Trail, then was found in Argentina with his Flaming Dancer friend, it sounded like his political career was over," Mr Trump tweeted on Monday.
"It was but then he ran for Congress and won, only to lose his re-elect after I Tweeted my endorsement, on Election Day, for his opponent. But now take heart, he is back, and running for President of the United States. The Three Stooges, all badly failed candidates, will give it a go!"
Mark Sandford, who announced on Sunday he would run against Mr Trump in the Republican primaries, was at the centre of a scandal when as governor of South Carolina he went missing for a week in the summer of 2009.
Before his disappearance, he told staff he would be hiking the Appalachian Trail, but later admitted to an affair with an Argentinian journalist after he was caught arriving back in the US on a flight from Buenos Aires.
Mr Trump's use of "flaming dancer" seems to be a misspelling of "flamingo dancer", which the president appears to wrongly believe is the name for a Spanish dance which is actually called flamenco.
The 73-year-old previously criticised Mr Sanford during a 2018 rally in Ohio as a man who likes "flamingo dancers from Argentina".
There is no evidence Mr Sandford's former mistress, María Belén Chapur, has ever been a flamenco dancer.
His use of the "three stooges" is a reference to three Republican candidates - including Mr Sanford - who plan to challenge Mr Trump for the Republican nomination.
Mr Trump had earlier retweeted a Twitter account titled "The 'Dirty' Truth", which prominently features links to websites promoting QAnon, a debunked, fantastical far-right conspiracy theory which claims there is a secret "deep state" plot against Mr Trump and his supporters.
The "Proud POTUS Trump & US military supporter" had posted a video in which Republican congressman John Ratcliffe criticised former FBI director James Comey during an interview with Fox News presenter Maria Bartiromo.
"Maria & John understood the dishonesty & deception from the very beginning!" Mr Trump added.
He concluded his rant with a false claim he has 94 per cent approval rating within the Republican party, wrongly stating it as a record.
Mr Trump is currently polling less than that in Gallup, Quinnipiac and Ipsos, and according to CNN, his peak popularity places him only sixth out of seven Republican presidents since the Second World War.
The president's outburst came days after former White House officials raised questions about the president's mental health.
Anthony Scaramucci, briefly White House communications director in 2017, and who now engages in public spats with Mr Trump, said on Friday his former boss was "in severe mental decline" and would "not make it" to the next election.
Another former aide told Business Insider: "His mood changes from one minute to the next based on some headline or tweet, and the next thing you know his entire schedule gets tossed out the window because he's losing his s***."
On Sunday evening, Mr Trump lashed out at a host of journalists and celebrities for his perceived lack of credit for US government efforts at criminal justice reform.
After attacking "boring musician" John Legend and his "filthy mouthed wife" Chrissy Teagen, the couple hit back, with Teagen branding Mr Trump a "p**** a** b****".
The hashtag #PresidentP****A**B**** was subsequently shared thousands of times by US twitter users.
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