I know a little bit about Hawaii, and I can say that keeping Hawaii Republican is going to be VERY difficult. There are two basic problems with it:
- The Hawaiian Democratic Revolution;
- and the right-ward shift of the Republican Party from the 1950s.
Herkles already mentioned this, but it's important to remember that the Republican Party in Hawaii was, from 1898 onwards, the agent or representative of the plantation owners and the monied, elite interests in Hawaiian society, which were mostly white and hence a relatively small minority both economically and ethnically. In that respect, it was somewhat like the Democratic Party in the South, except that instead of having a large poor white class it could enlist to reinforce its rule it had...well, nothing, really, I mean no firm
mass base of support it might be able to draw on. Thus, the moment that the Hawaiian and Asian majority were able to get their own people into power, which happened in reality in 1954, the Republicans were doomed to a long period in the wilderness in Hawaii. This actually happened five years
before the statehood vote, so I have no idea what the heck the people who thought that Hawaii was going to be "reliably Republican" were on. Anyone who spent a lick of time actually looking at the state's politics should have realized it just wasn't going to be so.
Anyway, although the Democratic Revolution pretty much rules out any
post-statehood PoD for your desired "Republican Hawaii," that hardly means it's impossible. It just means you have to go back...way back...and have the annexationists and hence the monied interests associate with the Democratic Party instead of the Republican Party. Don't ask me how that could happen, because I don't know, but I don't think it's impossible--as I said, the situation in Hawaii at the time reminds me somewhat of the South, and so there's no
obvious reason why they couldn't be entirely happy within the Democratic Party if they had swung that way. In this case, the Democratic Revolution, whenever it happens, will be more of a Republican Revolution, and will probably result in the election of a Republican or at least a Republican-aligned party (in the latter case, think the Minnesota Farmer-Labor Party--not formally part of the Democratic Party, but effectively so). Of course, then the conventional wisdom of ignorant mainlanders will probably be that Hawaii will be reliably Democratic, but you can't have everything.
The problem then comes in the evolution of the nationwide Republican Party subsequent to the Republican Revolution. Assuming that Hawaii having the opposite political orientation to reality doesn't drastically change wider American politics, which seems reasonable, the trouble is that Hawaii is sure to be rather on the left of the Republican Party, just by the nature of the islands and how the Republicans came into power. The inhabitants of the islands are going to want federal spending to keep flowing and a nice welfare state to take care of everyone who isn't an heir to the Big Five. In other words, the Hawaiian Republican Party, in this scenario, is going to be at its most right-wing Rockefeller Republicanism, which means that it's going to be going increasingly against the grain of the national party from 1964 onwards. I can see Republican domination lasting, in this scenario, into perhaps the 1990s just from inertia, but from that point on I think it's very doubtful that the Republicans will be able to hold on to a real dominance of the political scene, that is one where they operate without major opposition. Increasingly, I suspect, the Democrats will be competing with and defeating Republicans, who will be increasingly tarred with association with a national party that no longer seems to have much to do with what Hawaii wants and needs. By the present day the Republicans
might be holding onto a few statewide positions, but probably on pure incumbency, with little prospect of retaining their seats once their current holders retire or die.
Of course, you could have the parties evolve differently such that the Republicans become the liberal and the Democrats the conservative party, which would naturally tend to favor the Republicans in Hawaii. But how you do
that is a rather larger question that will have much bigger repercussions than simply keeping Hawaii Republican.