Over here, people are alreasdy hinting that the 'Partygate' investigations that contributed to the downfall of Boris Johnson were not properly conducted. I suspect these people of being Rishi Sunak supporters getting ready to undermine Liz Truss if she wins the leadership election (which seems likely).
Given that this sort of thing is SOP in politics, we can hardly blame Merrick Garland for taking time to dot all the i's and cross all the t's before proceeding to an indictment. Any case against Trump must be absolutely watertight and fully-evidenced, proofed against accusations of witch-hunts and political motivation. Because it will cause trouble and unrest among the infamous 'base', and when it does, there will be those in authority who might be inclined to turn a blind eye to it. An ironclad case against Truimp would leave those in positions of power who still support him two simple options: support the law by tackling the unrest, or openly defy the law and risk jail themselves.