Technically no, since defamation is a tort in U.S. law, not a crime. It must be privately prosecuted. However I appreciate the point you're trying to make. Previously, indictments in the U.S. against people currently outside U.S. jurisdiction have obeyed the law of nations and international law, and the sovereignty of other nations. Pres. Trump has indicated he will no longer respect the sovereignty of other countries, which may have disastrous consequences.
To save us the hypotheticals, here's the full text of the law under which Trump has accused Maduro:
https://www.law.cornell.edu/uscode/text/21/960a
In section (a) and the laws it refers to you can see what specific acts the U.S. believes foreigners can be held liable for, even if they occur outside the United States. One of them is a predictable wall of text alleging all manner of activity with harm against the U.S. or its citizens as its goal. In section (b) you can see why the U.S. believes it has personal jurisdiction over people who commit those acts, even if they commit them outside the United States.
Those provisions don't apply to every U.S. criminal law. The fact that they're outlined here in this section means their long-arm effect is limited to these specific acts. So no, you can't be dragged away from your sovereign home if you commit just any old act that happens to violate U.S. criminal law. Hence the one about owning a machine gun is especially stupid. It's generally against the law for a private citizen to own a machine gun
in the United States, but trying to say someone else in another country can't possess one because it's against U.S. law is daft and unsupportable.