[1] Klein is a published academic, having served as a lecturer at Temple University and as a biostatistician at the UCLA Fielding School of Public Health and the Linus Pauling Institute.

[4] Klein said in a Jewish Press interview regarding his father that "In Europe he had a long beard and black hat and was a rosh yeshiva in his early 20s.

He has served as a biostatistician at UCLA School of Public Health and the Linus Pauling Institute of Science and Medicine in Palo Alto, Calif.

[6] Today, Klein is member of the International Board of Governors of the Ariel University Center of Samaria.

[9] After the Obama administration abstained from using its veto power to block United Nations Security Council Resolution 2334 which stated that Israeli Settlement in the West Bank is a "flagrant" violation of international law, Klein called Obama "a Jew-hating antisemite.

"[10] Through the ZOA, Klein criticized Democratic congresswoman Alexandria Ocasio Cortez for using the phrase never again in reference to the Trump administration's immigration detention facilities.

[15] In April 2018, Klein tweeted: "Natalie Portman's absurd, uninformed, inaccurate, dangerous views on Israel, while ignoring the anti-Semitic, pro-terrorist views/actions of Hamas and the Palestinian Authority gives credibility and legitimacy to the ludicrous, false, nonsensical belief that beautiful women aren't too bright."

Portman had refused to accept the Genesis Prize in Israel, protesting the killing of Palestinian demonstrators on the Gaza Strip border.

"[19] In the context of the widespread protests following the police murder of George Floyd, the statements put Klein in conflict with more liberal Jewish groups.

Rabbi Rick Jacobs, the president of the Union for Reform Judaism, questioned the continued membership of ZOA in the Conference of Major American Jewish Organizations by saying "we are now implicated by his views, his Islamophobia, his racism, full stop.

"[24] Klein served as a lecturer at Temple University[25] and as a biostatistician at UCLA School of Public Health and the Linus Pauling Institute of Science and Medicine in Palo Alto, California.