Member of the Socialist Party of America, and former leader of the Communist Party of the USA.
Lovestone was expelled from the Commmunist Party for his support of Nikolai Bukharin, and for his theory of American exceptionalism. After his expulsion, he became an anti-communist, and even provided information on Communist labor unions to the CIA.
Jay Lovestone - Wikipedia
"Jews in Radical Politics" - MyJewishLearning.com