Truman decides that maintaining good relations with the Arabs is more important + Stalin doesn't veer towards antisemitism with the Doctors' Plot.
If Truman is too anti-Israel in 1948 he will lose the election and presumably Dewey will try to establish good relations with Israel.
Why do I say an anti-Israel Truman would lose in 1948? Well, he won Ohio by 0.24 percent, California by 0.44 percent and Illinois by 0.84 percent. Had Truman lost these three states to Dewey, Dewey would have 267 electoral votes--one more than the 266 needed to win.
https://en.wikipedia.org/wiki/1948_United_States_presidential_election Los Angeles, the Bay Area, Chicago, Cleveland, and Cincinnati all had substantial Jewish communities which could make the difference in such a close election.
As it was, some American Jews felt that Truman wasn't pro-Israel enough because (1) he only recognized Israel
de facto rather than
de jure; and (2) he imposed an arms embargo which was widely seen as favoring the Arabs over Israel. The Progressives in particular used the Israel issue against Truman; of course they could do so because the Soviets were pro-Israel. Leo Isacson's
https://en.wikipedia.org/wiki/Leo_Isacson upset victory in a congressional special election in the Bronx in early 1948 was widely attributed to Jewish dissatisfaction with Truman's Palestine policy ("Truman spills Jewish blood for Arab oil", etc.
https://books.google.com/books?id=oOaJCpyZFW8C&pg=PA76) It is very likely that the perception of Truman as insufficiently friendly to Israel cost him New York. (While some of the Jewish vote for Wallace was from leftists who would have supported Wallace anyway, Samuel Lubell and others have argued that some non-leftists also voted for Wallace because of the Palestine issue.)
As for Stalin, while Soviet relations with Israel didn't reach their nadir until early 1953, they were cooling long before that. The rapturous reception given Golda Meir at the Moscow Choral Synagogue in 1948 made the ever-suspicious Stalin doubt the loyalty of Soviet Jews well before the Doctors' Plot.
