[Joe 6-pack]

I would contend that the oath or affirmation provides for an ongoing, present condition or state. Until relieved of the oath or the swearing is found to be invalid (i.e. determined to be a lie), his swearing continues, thus, “he swears.”

[Bloody Sam Roberts]

I suppose I will have to defer to your explanation. The more I read that damnable sentence the better it looks.

Perhaps if the word 'repeatedly' weren't there, I could make a better case.
Aye, therein lies the rub.