Sue for fraud, malfeasance or whatever the law allows.
That brings the powers of discovery which gives huge power to dig into every nook and cranny.
If you have secrets, civil suit is far more to be feared than a criminal charge because of the many restrictions the courts have put on criminal prosecutors, investigators, etc.
Lawsuits are the only way. The favored tactic of the left has to be employed against them since Republicans cannot be counted on to do their jobs and the media determines their direction via hit pieces and pressure.
In every state there is enough money going to worthless GOP candidates that people would be better served feeding to a complete shark tank of a legal team. THEN we would see results and Democrats in prison garb.
Civil suits can quickly lead to criminal charges with the right people pressing the issue.