Of course the US has acknowledged the ICC.

In 2002 on the heels of 9/11 George W Bush signed https://en.m.wikipedia.org/wiki/American_Service-Members%27_... into law, also known as Hague Invasion Act, specifically acknowledging the ICC in the clearest of ways.

If there is a nation that cannot be expected to act with equanimity in regards to Israel, that's Germany. Nothing to do with the legitimacy of the ICC, that Germany has always recognised.

Is this something the German chancellor can say? In countries with an independent judiciary, this is a matter for prosecutors, police and courts.

In most countries state prosecutors are directly controlled by the executive. The US is a bit of an anomaly in having semi-independent elected prosecutors. The government wouldn’t normally get directly involved - the optics are terrible - but in high profile political cases they will.