The conservative commentator - a one-time Mr Trump ally turned fierce critic - told the paper that she thinks his dominance in the Republican party is over.
“Trump is done,” she said in an email. “You guys should stop obsessing over him.”
Her comments came in an article about the rising tensions between Mr Trump and Florida Governor Ron DeSantis as speculation grows that the two may go head-to-head as Republican candidates in the 2024 White House race.
The former president is said to have been complaining privately for some time about the governor’s rise within the GOP and his refusal to rule out a White House run if Mr Trump joins the race.
Last week, tensions behind the scenes entered the public sphere when Mr Trump made a thinly-veiled jibe about the governor’s refusal to say whether or not he had received a Covid-19 booster shot.
Mr Trump said in an interview with One America News Network that politicians who dodge answering the question are “gutless”.
“I watched a couple of politicians be interviewed and one of the questions was, ‘Did you get the booster?’” Mr Trump said.
“Because they had the vaccine, and they’re answering like – in other words, the answer is ‘yes,’ but they don’t want to say it, because they’re gutless. You gotta say it, whether you had it or not, say it.”
Many viewed his comments as a direct attack on Governor DeSantis who has been asked multiple times and has swerved giving an answer each time.
Last month, the governor told Fox News: “I’ve done whatever I did, the normal shot.
“And, you know, that, at the end of the day, is people’s individual decisions about what they want to do.”
Ms Coulter picked up on the spat and called Mr Trump a “liar and a con man” on social media on Wednesday.
“EXCLUSIVE: Trump is demanding to know Ron DeSantis’s booster status, and I can now reveal it,” she tweeted.
“He was a loyal booster when Trump ran in 2016, but then he learned our president was a liar and con man whose grift was permanent. I hope that clears things up.”
EXCLUSIVE: Trump is demanding to know Ron DeSantis's booster status, and I can now reveal it. He was a loyal booster when Trump ran in 2016, but then he learned our president was a liar and con man whose grift was permanent. I hope that clears things up.
— Ann Coulter (@AnnCoulter) January 12, 2022
Ms Coulter famously championed Mr Trump’s first run for presidency, releasing her book in 2016 entitled In Trump We Trust, E Pluribus Awesome!
In the book, she hailed the Republican candidate, pointing to his promises to stop immigration into the US and build a wall along the border with Mexico.
But, since then, Ms Coulter has become one of Mr Trump’s biggest critics, publicly slamming him on multiple occasions.
Back in November, she said that she was “familiar with what a narcissistic, ridiculous, tacky, vulgar, arriviste this guy was” when she endorsed him but “had no idea how abjectly stupid the man is”.