I think what they meant is that Trump is effectively executing on his unserious policy. Not being serious as in being a serious person, but serious as in actually doing the demented things he promised.
It's not only American news media that wears blinders. The conservative German national daily, the FAZ, chose to downplay this historic rebuke of the right and play up Trump. With Google Translate:
Google translation of a Zeit headline: The difference in Germany is that 12 members of the conservative parties voted against their leader. If only so-called conservatives in America had a gram of courage.