On a federal level, there really isn't much they can do that I'm aware of. It would have been nice to see them blanket oppose Trump's cabinet picks but that would only be symbolic since they don't have the numbers. They can't get any laws passed, and even if they could, Trump has no qualms about disregarding the law, which the Supreme Court says is fine.
If they wanted to go outside the law I guess they could try to organize some kind of coup, but failure at any stage would not only be career suicide but possibly actual suicide given that treason is punishable by death, and this administration would be gleeful to carry out that sentence against Dems. And if it did succeed, that still wouldn't do anything about the oligarchy propping up Trump, they'd just have another puppet (Vance) to fall back on.
They're not throwing flaming oil though. They didn't even pour oil onto an enemy and light them on fire. They poured oil onto a weapon rack then lit that on fire. The enemies can simply not interact with the fire if they don't want to. A DM can rule that a series of events together might constitute an attack because it resulted in something similar to an attack (because a DM can rule anything they want), but compounding actions and classifying them based on their result is not covered within RAW.
The difference between those scenarios you've invented and the scenario in the post is that pouring out oil and lighting a fire with a tinderbox already have existing rules, there's no need to try to interpret the mechanics of the situation.
Only if the roll made is an attack roll. As OP says, pouring out a flask doesn't require an attack, nor does lighting something with a tinderbox. In fact neither of these should require any roll at all.
I'm going by 2014 rules, but what constitutes an attack is actually pretty strict. Basically, there must be an attack roll of some kind, or the rules for that action must specifically describe it as an attack, for it to actually be an attack.
On a federal level, there really isn't much they can do that I'm aware of. It would have been nice to see them blanket oppose Trump's cabinet picks but that would only be symbolic since they don't have the numbers. They can't get any laws passed, and even if they could, Trump has no qualms about disregarding the law, which the Supreme Court says is fine.
If they wanted to go outside the law I guess they could try to organize some kind of coup, but failure at any stage would not only be career suicide but possibly actual suicide given that treason is punishable by death, and this administration would be gleeful to carry out that sentence against Dems. And if it did succeed, that still wouldn't do anything about the oligarchy propping up Trump, they'd just have another puppet (Vance) to fall back on.