Sometimes a resignation letter gives a specific date or even a time. For instance, Rep. Chris Lee, R-N.Y., resigned effective 5 pm on the day pictures of him surfaced.
A letter may even say something as simple as "I resign."
So, until that letter is made official by reading it on the House floor or notification of the time or date the resignation is effective, Anthony Weiner remains a duly-elected and sworn Member of Congress.
And Weiner didn't have to resign Thursday. In fact, it is entirely possible that he could serve out the rest of his leave of absence and then resign.
But even if a resignation letter does surface Thursday, it will not be reported on the House floor until next week.