I'm a PhD student focusing on Nixon's vice presidency, but the presidential stuff is really interesting. The difficult thing with books on Nixon is that you're immediately confronting either vehemently pro or anti Nixon types. Beyond that, there wasn't really much of a "power struggle" given that Nixon was more getting caught possibly abusing power than struggling over it.

The issue at hand here was more one of where the most power resides in the American system: the executive or the legislative branch. And most of the resultant blow-back really came after Nixon had resigned, and had to be dealt with by Ford and Carter. And in any sense, whether you're mostly interested in Watergate, the aftermath, or the centralization of decision-making in the Nixon White House, there is no one book that deals with that properly or fairly. The biggest challenge is that, essentially, when Congress decides to assert itself in a fairly unified manner, the President is at a real disadvantage. FDR encountered something like this when the Supreme Court struck down the first New Deal, but that's obviously the judicial acting against the executive and legislative rather than executive fighting legislative.

I guess a good place to start either way would be Nixon's memoirs (RN, second volume) as that will give you, at the very least, Nixon's account. I'd generally avoid Kissinger, not because he isn't useful but because on almost every topic, he just gives a typical Kissingeresque analysis (more details about why he deserves credit if the outcome was good, or why he doesn't deserve blame if the outcome was bad). A good example of this is the Chilean affair. Nixon devotes maybe a paragraph of his memoirs explaining essentially that his actions in influencing the downfall of Allende did not deviate from past American actions, and that there was real concern that Cuba and the Soviet Union were exercising undue influence. Kissinger says essentially the same thing, over forty pages, whilst crediting himself for keeping U.S. actions honourable and effective. After RN, I'd recommend Stanley Kutler's Wars of Watergate, Anthony Summers's Arrogance of Power is a fun anti-Nixon book (if you couldn't tell by the title), and I can list more if you'd like.

If you're interested more in the executive clashing with the legislative, I honestly think Andrew Johnson's tenure as president is still the absolute best case study one can examine. With Johnson you have a man that everyone thought would act one way, who acted almost completely against these perceptions, and who came closer even than Nixon to being impeached. This was an actual power struggle as you had Johnson openly trying to divide the Republicans, while courting ex-Confederates, Democrats etc., basically looking to impose the policies he thought best for America.

Eric Foner's book on Reconstruction or McPherson's Ordeal by Fire are both okay for this topic, but David Stewart's Impeached is probably one of the better ones just on Johnson and the trial.