American public opinion may have expected such invasions, but did any serious military experts? Earl Warren and FDR's political pandering is not really strong evidence of a serious military expectation. Obviously, we know now that the Pearl Harbor attack was at the outermost of Japanese logistical capacity - they never planned an invasion of Hawaii, much less the West Coast.

There were proponents of an invasion of Hawaii within the Japanese military cabinet; I think Genda Minoru was one of them. Plans existed, but were deemed too risky and unlikely to succeed.

I never said anything about an invasion of the US West Coast, but the Japanese invasion of the Aleutian islands was supposed to be the first stage of an invasion of Alaska. Had that plan succeeded, Japan would have been in control of naval bases within reasonable distance of the US West Coast.

Given the history, we know that transpacific projections of land forces were very possible for the United States (Guadalcanal, Iwo Jima). Why would an invasion of Hawaii be more difficult?

Guadalcanal and Iwojima were within range of US forward bases. Carrying out a large-scale invasion over a distance of about 4000km is not something any military power was capable of during WW2, to my knowledge.