“President Johnson as well as the French and English were not prepared to intervene in any meaningful way”
It was in fact De Gaulle who precipitated the Six Day War through his withdrawal of support for Israel. Had he lost the 1965 Presidential election to the pro-Israel Socialist Mitterand, Israel would still have had France as an ally.
Johnson couldn’t do anything concrete because of Vietnam. (The UK was also in a similar situation in Yemen.) But he tipped off Israel to the fact that Egypt was planning an attack. Israel pre-empted and the rest is history. Thank you, President Johnson. (Johnson also had helped save some Jews from the Shoah and had condemned the awful treatment of Israel after the Suez War by the Eisenhower-Dulles Administration.)