They have only seven months to go, and as far as I can tell, haven't played out their last delaying action just yet, because the R's haven't pursued this vigorously enough to force them to do so.
It would not surprise me at all if this whole issue is being kept in reserve until the election looms closer. At that point, the burden of truth (at least in the eyes of the public) will shift to the accused, at which point a cornered politician might feel he has no choice but to claim executive privilege.
Which, in the eyes of the general public, would be an admission of guilt.
Of course, that cheapens the entire issue and the underlying tragedy, but that's the way things go in politics.