I suspect Harald “Hardrada” would totally be incarcerated in a Supermax prision were he alive today - where he would no doubt rule the hard-cases inside. 
Legal or not, it was a bad move and set a bad precedent. If I were living during the time, I’d have been against him, because I like the Constitution more than Lincoln.
Relevant L&O:CI quote:
Ron Carver: So your answer is to conspire to suspend his right of habeas corpus?
Judge Freeman: Get off your high-horse, Mr. Carver, even Lincoln suspended habeas corpus.
Ron Carver: Am I supposed to fall to my knees at the mention of the "Great Emancipator?" Even great men go too far, your honor.
Speaking of American political figures - I doubt these days whether anyone would get away with only a $300 fine for viciously beating a US Senator right in the Senate chamber because they didn’t like his speech. 
Harald Hardrara was killed at Stamford Bridge, so I’m not sure that he really fits. I thought we were talking about people who escaped punishment.
Not sure “death in battle” is a form of judicial punishment, exactly …
Aaron Burr. Most Veeps don’t kill people while in office any more.
Yeah, but per the OP, this is a modern-day Caligula. We have to gloss over the fact that there isn’t a Roman Empire in the 21st century, and imagine that somehow Caligula gains political power in the known structure of the 21st century and still does what he may have done in the 1st century.
I do like the idea of a President Caligula ordering that section 16 of the crowd at Nationals Park be thrown to the lions, and his 21st-century aides being like “WTF?” and promptly locking him away in the looney bin rather than the depressing reality of his 1st century aides making it so.
Sure. Just pointing out that he didn’t exactly get away with his antics it in the 1st either. The comeuppance was just of the, you know, stabbier and more extra-legal sort.
While we’re on the subject of Roman Emperors, Theodosius I probably deserves a mention for the “oops, I seem to have ordered the massacre of 7,000 race fans in Thessalonica” incident.
Consequences? Well, he felt really bad about it, and ended up grovelling a bit before Ambrose, the bishop of Milan, to save his soul. That’s about it. No stabbing.
The same could probably be said for Alcibiades.
Sorry I can’t tell–is this a joke?
The invitation from Parliament trumped everything else. Don’t forget that Charles II (and hence James) only became king because Parliament had invited him back after the collapse of the Commonwealth. Also, FWIW, William, as their nephew, had been the nearest to a male heir (until the Old Pretender was born to James’s Catholic second wife), which was perhaps one of the reasons why James’s daughter had been married to him. And, of course, see the comments above on Henry VII - it was a coup d’etat, but a parliamentary one and retrospectively legalised by the Bill of Rights.
Treason never prospers -
What’s the reason?
If it prosper,
None dare call it treason
If modern-day Lincoln suspended habeas corpus under the same conditions (a civil war, Congress not in session) nothing would happen. No one has been or will be prosecuted for torture, or the collection of mass data on every American without warrants. If you do it to “keep America safe,” you’re going to get away with it–whatever the merits of your argument.
Well, no. But the thing about being dead is that you can’t go to prison. 
Hardrada probably would have been stuffed in some dungeon if he hadn’t been killed, is the point.
Doesn’t that same objection apply to many of the suggestions above? Can’t send Caligula to jail after sticking eight Praetorian swords through him, either.
Anyway, I was thinking more about Harold’s career prior to invading England - everywhere he went, he was a successful criminal, if his saga is to be believed (until he went that one step too far … )
Hardrada would have been killed if he hadn’t been killed. What would be the benefit in keeping Hardrada around if he had survived the battle? You’d just be creating the possibility that opponents of your reign would free him and use him as a rallying point against you. (As it was, even with both Hardrada and Harold dead, William still had to deal with several claimants challenging his rule.)
It would, too, because there’s no civil war going on today. It would also be illegal for George Washington to own slaves today.
I think we just take it as read that conditions are as they were when he did it.
That’s a bit like saying that Aaron Burr wouldn’t be arrested for killing Alexander Hamilton today, because Hamilton died in 1804.
Jesus Christ would have been guilty of, at the very least, disorderly conduct for creating a ruckus at the ancient Temple.
Since it was likely his first criminal offense (under secular, Western law, that is), he’d have probably gotten probation.