Presumably because they knew that the allegations would not be credible.
Either way, that's how the system works...we vote. The allegations will keep coming. Announce a vote date to force the Dems to show all of their cards (trot out all of their recruits at once), and then vote on it. If the Dems want to, they can impeach him later. But, they won't unless they get something better than they have at this point...which is why they want to stall now.
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