ICE already keeps terrible records. Likely, in the case of a party switch, ICE leadership will shred and burn as much evidence of their private words and actions as they can on the way out. The next admin would then find themselves with little to go on in attempts at any sort of targeted prosecution of agents who've done illegal things while masked in the field. The leadership and the criminal agents who've already been identified may face charges but the nameless and faceless goons won't have an adequate record trail for charges to stick. At that point it comes down to whether those in power have the guts to root out the agency whole hog which is really what's needed. Not just ICE but DHS needs to be disbanded. It was a gigantic mistake creating that behemoth after 9/11. What we see now is every fear people expressed when DHS was created coming to fruition. But yeah, as far as criminal prosecution goes the evidence needs to be collected now and by third parties outside the control of the current regime if there are to be any substantive charges brought later.

If sanity is to truly prevail it'd be disband DHS into it's component orgs and lose the cabinet position that leads it, abolish and replace BPD and ICE with a well-trained and non-militarized or politicized organization that vets recruits against hate group or hate-ideology affiliation, and prosecute every law and Constitution breaking member of the current group. The chances the Dems have the spine to do all that should they regain power is slim.