>Japan First" doesn't have to mean your naïve interpretation of some maximally xenophobic isolationism.
It doesn't. But it probably will, especially with Japan's history. How many times does history have to repeat before we stop dismissing it as a slippery slope?
>many also believe that the US alliance and the bases are critical to Japan's greater sovereignty and prosperity.
America stripped their standing army for decades, so that damage is inflicted by the very ones that claim to protect them. And the US isn't exactly a reliable ally as of late.
Not wanting huge numbers of foreign army base in your country is Xenophobic Isolationism ? I'm sorry; I guess I'm all hopped up on the the anti-colonial struggles of Asia (ironically, many of them, supported by Japan).
The China issue is orthogonal to all this. US-Japan relations were atleast beneficial till now (unlike say Europe's colonial possessions in Asia), but it looks like the country will first suck all its vassals dry before going down.
Some people might disagree—certainly plenty of right-wing Japanese do disagree—but many also believe that the US alliance and the bases are critical to Japan's greater sovereignty and prosperity. Without the security treaty and cooperation, Japan would on their own against China, diverting far more funds to defense and accepting much higher security risk.