Not at all. If there is an open ended declaration of war in the war on terrorism(which there is), and they are officially declared terrorist(which they are) that means that they fall under the articles of war and all of the laws and limits of those laws apply. I like the way Admiral Holsey put it where he explained that we cannot expect our own solders to be treated in accordance to the laws and regulations of war if we do not set that example ourselves. The decision by Trump was to declare them as terrorist because it falls under that congressionally approved declaration of war. That means he has to follow those rules or face war crimes if not.
Nah this is a really bogus claim to suggest it is a war crime especially after a lot of subversion in the past. This will just encourage Trump to crack down on the subversives harder, and also drive the population at large to support Trump more actually and distrust the democrats even more. I understand your premise if we remove the idea of war crimes, it is philosophically sound (ie: the principle of reciprocity, that if we take extreme measures others will too.) The situation though is that Venezuela has become so extreme that intervention is neccessary. Maduro's reign and also foreign activities, not just against the USA I would add, constitute a valid neccessity for the USA to intervene. From both a purely internal nationalistic narrative Trump is in the right pretty solidly, but also accounting for the international dynamic it's kinda like Maduro has run out of his last excuses. No one will actually stand up to the USA for him because he's an idiot dictator whose incompetence and corruption is so vast it's actually quite evil. I mean here's a guy who is functionally a billionaire via narco-terrorism while for a comparative middle class job a regular person earns $5 a month. You factor in his aggression lately not just in threatening Puerto Rico and the USA, which is almost laughable, but also his weaker smaller neighbor Guyana which very much is kinda helpless against his overt aggression. Then simply in the matters of removing him, we don't really need a declaration of war or to repeat Iraq and Afghanistan (which I presume mutally we both don't want that.) We just need to simply kill Maduro or convince him to surrender himself or flee into exile, and pretty much literally any person or faction will do a better job than him because he is the literal record holder of incompetence and corruption.