Why would it matter whether his political party is on board? The GAO puts out a report regardless of whether it expects one party or the other to disagree with it.

The GAO is not associated with a political party. It meets that definition. In particular:

> in most cases, nonpartisan refers specifically to political party connections rather than being the strict antonym of "partisan".

If the Trump EPA says the sun appears blue to everyone, then is it a partisan issue to say they're incorrect?

Partisan means pushing a political agenda based on ideology or party. NOT that a particular party agrees or disagrees with them.

You're using the straw man argument, which is vacuous. You are also ignoring the correct definition of nonpartisan, which I linked above.

Not much of a straw man, since we are nearly certain about the fact that mean temperatures are rising as we are about the color of the sun.

Whether or not the changing climate is anthropogenic is somewhat less certain, (and more politically contentious), but we ought to be able to discuss the effects of these absent the cause without calling a report partisan.

It's called analogy, and I believe I am still correct. If a report aligns with a particular party, that does not make it partisan. The motivations and affiliations of an organization may make it "left leaning" or "right leaning", but the GAO is pretty well established as non-partisan.