There are two basic ways to develop a topic. (I'll get to "nuanced research question" in a bit) - via primary source analysis or finding holes in historiography. Obviously both need to come together, but you'll probably start with one, or at least start primarily with one.

Historiography is probably going to be easier in your case. Read the latest and greatest scholarship on Kissinger. (Or, because he is very very studied, something like "war and game theory in modern U.S. history"--the different ways it's been applied. Finding a new way to apply that sounds like something that would be up your proverbial alley!). Do authors comment on what someone needs to do/where research might go? What questions do the books and (especially, because there's a faster turnaround) articles leave you with? Did you read any studies where you think, "Okay, that's not quite right with the analysis of X body of sources"?

One paper of mine came into place when I realized 99% of modern scholarship on a particular figure was grounded in some fundamental misreadings of a key primary source. Another was "here are two competing perspectives about a topic. They can't both be right. [reads primary sources] Hey, they're both wrong because they didn't look at all the evidence!"

I am a medievalist, so I really can't comment on what it's like to work with modern U.S. primary sources. I imagine you'd need good experience with the historiography to know what's out there, though.

As far as getting to a research question: I like starting out with a general one, and then seeing where my research (primary sources in particular) is taking me/telling me the story is. So I might go from "did women have a Reformation?" to "what is this woman's religious experience" to "what is this woman's social experience of religious change" to "OMG look at how this person understood and manipulated the socio-religious context to achieve her goals!" And then followed by several evolutions of, you guessed it, how that person understood and manipulated etc.

Generally I will start writing when I am two to three stages away from my final, actual question-thesis. I throw away a lot of pages, in the end, but the final product is better. This has been true since my freshman year of college. (I do think my high school history papers ended up where they started.)

ETA: I think I can retrace the steps of my example more clearly:

• General interest: "women in the Reformation era"

• Reads some scholarship. Debated question never definitively answered: "Did women have a Reformation?"

• Realize topic is unmanageable. How to address it in a form I can deal with? Look at one woman.

• Read (very small) body of primary sources. Obvious question: "What is her religious experience like?"

• Read secondary scholarship. Discover everyone talks about her religious beliefs. Hrmph.

• Reconsider sources. More specific question arises. "What is her social experience of religious change?"

• Reread sources with that in mind. Discover OMG HERE'S HOW SHE MANIPULATED IT, HERE ARE HER GOALS.

• Calm down. Reevaluate, write, reevaluate, write, reevaluate, write.

• Beg for extension.

• Reevaluate and write for real.

:)

I would echo what /u/sunagainstgold said, but also suggest that you look at what the National Security Archive has recently released through FOIA requests. Freedom of Information Act requests are constantly being submitted and new documents are coming through all the time. Some groundbreaking, others not.

If you want to study Kissinger, I'd suggest you contact Peter Kornbluh of the National Security Archive (along with a professor who studies US foreign policy) to ask if he knows of any recent releases that might make for an interesting investigation. Kornbluh specializes in Cuba himself but being the head of the National Security Archive (an NGO) he is aware of interesting finds. New info is coming out constantly and I'm sure they'd be happy to share leads that would lead to someone systematizing recent discoveries. Peter is also a great guy and could probably point you in the direction of a specialist who also works Kissinger with the idea that he give you some pointers.

In regards to 'how to land on the question' behind the thesis, the methodology I was taught was based on solving a 'problem'. Figure out what question you're trying to answer with your research, then reflect on it and see if there is an underlying issue that is even more important and which your research could speak to. For example, 'did Kissinger have foreknowledge about X or Y human rights abuse', which could be turned into 'what are the legal implications of Kissinger's foreknowledge of X or Y human rights abuse'. Always frame your investigation and line of questioning in terms of burning questions within historiography. Find out what is hotly debated and see how your research could speak to that debate.