Option 1 was “let it go ahead”. The consequences of that seemed to the GQP tacticians to be extremely bad.
Option 2 was “block it” which they chose. The consequences of that fork into two paths:
Path 1: The Dems give up. Consequences from that are minimal. This is the “best worst case scenario” and they can only get it by blocking.
Path 2: The Dems field an non-bipartisan “study” of the situation. This gives two bits of ammo to the GQP: They can scream about how it’s partisan and unethical and a big lie and nobody should trust the outcome. AND they get to lie to the investigators without being under oath because it’s not a “Congressional” investigation. This path, too, is much better for the GQP than option 1.
Bottom line: there is NO real downside to liars and cheats who block the investigation. Of course they blocked it.