Quoting Wikipedia:
“In the 1973 Yom Kippur War, Arab forces were overwhelming Israeli forces and Prime Minister Golda Meir authorized a nuclear alert and ordered 13 atomic bombs be readied for use by missiles and aircraft. The Israeli Ambassador warned President Nixon of "very serious conclusions" if the United States did not airlift supplies. Nixon complied“
What if the US hadn’t helped Israel? What would have happened? Would the Israelis use only tactical nuclear weapons on the advancing enemy armies or would they go directly for their capitals?
In any case, how would the Soviet Union react?