Trump conspired to defraud the United States. The biggest obstacle is always criminal intent/state of mind.
The January 6th hearings have offered compelling evidence that Trump clearly knew his Big Lie nonsense was in fact a Big Lie. He took way too many steps thereafter to stop the certification of the electoral count (to include meddling in state counts in GA and AZ) and chose not to marshal resources to quell the mob storming the Capitol on January 6th. The DOJ will need 5-7 solid witnesses and co-conspirators -- who were in the loop. The DOJ will also unimpeachable corroboration to overcome defense attacks against those testifying witnesses.
It is an unprecedented fact pattern. Unprecedented occurrence.
We ought not underestimate Garland's tenacity and determination if, I say again if, the evidence to prove the conspiracy is jumping off the plate.