This might be it:
https://www.newyorker.com/magazine/2012/10/08/super-rich-iro...
> Last July, before he had written the [harshly critical] letter [about Obama], Cooperman was invited to the White House for a reception to honor wealthy philanthropists who had signed Bill and Melinda Gates and Warren Buffett’s Giving Pledge, promising to donate at least fifty per cent of their net worth to charity. At the event, Cooperman handed the President two copies of “Inspired: My Life (So Far) in Poems,” a self-published book written by Courtney Cooperman, his fourteen-year-old granddaughter. Cooperman was surprised that the President didn’t send him a thank-you note or that Malia and Sasha Obama, for whom the books were intended as a gift and to whom Courtney wrote a separate letter, didn’t write to Courtney. (After Cooperman grumbled to a few friends, including Cory Booker, the mayor of Newark, Michelle Obama did write. Booker, who was also a recipient of Courtney’s book, promptly wrote her “a very nice note,” Cooperman said.)
Here's a more recent retelling:
https://www.vanityfair.com/news/2019/10/leon-cooperman-eliza...
> For those unfamiliar with Cooperman’s history of bitching and moaning, this isn’t the first time he’s complained about being treated just sooo unfairly by a politician. During the Obama years, he claimed that the president’s description of Wall Street leaders as “fat cat bankers”—made in the immediate wake of the financial crisis before he would go on to be extremely business friendly—was encouraging “class warfare,” and that Obama’s “polarizing tone” was “cleaving a widening gulf…between the downtrodden and those best positioned to help them,” i.e. the rich. Speaking of tones, Cooperman, like many of his brethren, chose to liken Obama to Adolf Hitler, and also got his knickers in a major twist over the fact that the president had the audacity not to write a thank-you note to Cooperman’s 14-year-old granddaughter for her unsolicited book of poems. So Liz Warren better shape up, and fast.