Yeah, I think that threats against the president should be taken seriously, and if there's a legit way of taking this painting as a threat against Trump, it should be investigated.
Seems like an artist's attempt to make a political statement and he uses things like decapitations, captain america, and other symbolic things to drive it home. I'm no critic and I won't try to say whether it's good art or not, but it certainly seems to have made people talk...but it seems like some of that conversation is going dangerously close to the kinds of reactions we'd expect from Muslims who call for the murder of cartoonists who portray Muhammad. It's not quite that extreme, but if we're inching closer to a position where folks can't be blasphemous towards religion or public figures (so long as there's no real desire to incite violence or threaten folks), then it seems a step in the wrong direction imo.