The US should never bow to the terrorist or the threat of terrorism, if these were Muslims so Middle East country would be getting it right now.
Using this as an excuse not to invoke the 25th amendment is cowardly....if that’s the reason
TBF there is a considerable degree of sense in not forcing this through and allowing Trump to easily claim (though he might do anyway) that he* has no option but to save the Republic by a revolt.
If his lot aren't going to 25th Amendment him, then make sure he can't do anything for the next nine days and do what Manchin suggested - get Bidens' government in place first and then deal with this. As I've said previously I don't even think they need to set a precedent of locking him up, just have a release of what he's actually done these past four years and then let the GOP explain why it was they went along with it.
Going down the political gesture road (as impeachment will be, at least now) is daft.
* ie: his supporters, obviously not him personally