It's not clear to me that donating to politicians necessarily buys you clemency (in the absence of explicit quid pro quo), but accepting the premise, I think at a certain point, when your crimes and donations are widely publicized, there's a phase transition where it's more likely to work against you. The politicians can't bare the perception of having been bought, and whatever influence they're able to muster is directed against you.

But it's not clear to me that donating to campaigns in a handful of election cycles buys you very much influence within the DoJ. Influencing politicians in order to impact the nomination of judges or other appointees, or to pass certain laws - those are clear mechanisms, but they take many election cycles to implement. It seems to me like SBF's influence campaign was successfully building good will for the crypto legislation he supported, but that FTX/Alameda blew up before that could come to fruition.

I expect his donations to be largely neutral to his potential prosecution but am open to reporting surfacing facts to the contrary.