Rick Hertzberg provides a memoir. I don't think it's necessarily a sign of insincerity that someone's views have evolved over the years. The danger is always, rather, calcification of thought and socialized group-think - what we used to call the neocon slide (the ten minutes when a liberal-becoming-a-conservative was interesting). In the polarized politics of the past couple of decades, it has been very hard to sustain a complicated politics and have a social life in Washington. In that respect, I don't think Charles has changed that much. He remains a believer in science and evolution, I'm pretty sure he's an atheist or what the English might call a High Jew (no, not Bill Maher), he just wrote an article suppporting a big increase in the gas tax (not exactly a base-pleaser) and does not fire-breathe against gays.
Yes, he went soft on Bush's fiscal liberalism - but given Bush's total support for Israel and launching of the Iraq war, it was not a hard call. Yes, there's something rich about Krauthammer's hand-wringing about socialism now. But it's not quite as preposterous as it is coming from some others.
Charles has also been a consistent believer in almost limitless executive power in foreign affairs, and a passionate defender of maximalist Israeli positions with Safire/Podhoretz like levels of commitment. We were both passionate anti-Communists in the day and the one issue I remember having a big fight with him about in the 1980s was the Iran-contra affair. I was a squishy supporter of the contras but found the Reagan administration's illegal contempt for the Constitution and the Congress an outrage. Charles loved it. I also believed in a modest, realistic role for the UN. Charles wanted to abolish it. Later, I found torture to be an ethical and moral deal-breaker for supporting any coherent war against Jihadist terror. Charles saw it as just another tool against the enemy. Some things don't change.
It's just very hard to be that integrated into the Washington Republican Right and be able to resist the orthodoxies the party needs or the mood the party is in. It's subtly corrosive of truly independent thought. Some would argue such thought is naive for political life. I haven't given up that much yet. And all my closest friends have nothing to do with politics. That helps.