I think at this point it's simple preservation.
They know the success of the RNC convention, the popularity of President Trump in the polls, and the collapse of the Democrat party over hiding the true state of Biden's health.
I think they concluded that their best path here is to not be obstructionist when investigating an assassination attempt on President Trump or they would be seen by the American people as endorsing it.
-PJ
Good, thoughtful and reasonable analysis.