Serious question: At what point do republicans and the media admit that this guy is insane?

I think when he actually does go into a country, "guns-a-blazing."

Trump frequently makes threats. He seems to have no compunction about whether or not he will stand behind the threats he makes - for example, he has threatened Hamas several times, but no one seriously believes there's any likelihood that Trump will send U.S. troops into Gaza.

Trump believes - probably foolishly, perhaps even naively - that such threats are useful and effective tools of foreign policy, even though they are mostly empty threats. They are not always completely empty. In situations where the U.S. can use military force without any possibility of U.S. casualties (like blowing up fishing vessels from a distance), and against countries that cannot plausibly retaliate or escalate (like Venezuela) those threats are more credible - but only to the extent of action that cannot result in U.S. casualties. Since there is only a limited set of circumstances where such threats are credible, most of his threats are dismissed as empty.

Since Trump shows no signs of believing there are any long-term costs to U.S. credibility from making empty threats, his practice of frequently making them is not "insane." It's just wrongheaded and stupid. If he were to actually launch an invasion of Venezuela or Nigeria, that might generate more of a reaction from Republicans and the media.