On This Day in History

[Pergamos]

I usually hear "crossing the rubicon" as doing a big thing, that can't be taken back.  I've never heard it as specifically heroic, although sometimes it is, in context.  I also don't hear it in specific context as ending a republic, or anything else about the results of the action, that's specific.  it's always just a big, irrevocable, act that commits someone to a conflict in a way they can't take back.

Invading Greenland would be Trump crossing the rubicon, destroying NATO and whatnot. 

[Abbot Mythos]

I usually hear "crossing the rubicon" as doing a big thing, that can't be taken back.  I've never heard it as specifically heroic, although sometimes it is, in context.  I also don't hear it in specific context as ending a republic, or anything else about the results of the action, that's specific.  it's always just a big, irrevocable, act that commits someone to a conflict in a way they can't take back.

Invading Greenland would be Trump crossing the rubicon, destroying NATO and whatnot. 

I agree with your assessment of how the phrase "crossing the Rubicon" is used by us, and what it is perceived to mean to us.

And, while I make no claim to be an expert in Roman history, it is an interest of mine. And, it is my understanding that the ruling class of the Late Roman Republic would have judged a general officer who had "crossed the Rubicon" at the head of his army, as Caesar famously did, to have committed an act of treason. So, without me being too long-winded about it, I believe the phrase "crossing the Rubicon" had an altogether more sinister meaning to an ancient Roman than it does to us.

For what it's worth, I only started taking an interest in Roman history, during my hitch in the Navy, after I first saw for myself some of what the Romans had built in Greece, and then a small fraction of what they had built in Italy. Before that, I thought anything "Roman" was only important to Roman Catholics and Italian Americans.