You asked this question yesterday and received multiple answers, but you did not reveal in that post your tenured status.
Tenure, whether by way of federal civil service protection or another mechanism, can make a significant difference in both the process and the outcome that will apply here. Unlike an "at will" employee, you can be terminated only for cause and only after an administrative procedure that allows you to challenge the allegation by the employer of cause. In fact, the process and standard of proof re termination is very likely to be almost identical to that applicable to your appeal of the proposed removal of your clearance.
You are entitled to the assistance of counsel in your appeal of the proposed termination, although not one at public expense. If you are represented by a union, your union will ordinarily provide you an advocate or attorney. You may need to be assertive and aggressive with your union.
Be careful not to invest too deeply in the defense that the alleged offense is "trivial." It is not the judgment or the assessment of the employee that will determine the seriousness of any allegation of misconduct. That determination will more likely be adjudicated by the standards of the employer. But you are entitled to challenge the truth and significance of the facts alleged against you, the degree of penalty that is justifiable, your culpability, any factors of mitigation, etc.
The employer is not ordinarily required to maintain your employment while your clearance appeal is pending. The employer has the capability to restore your employment and to make good on any back pay and benefits if the appeal is determined in your favor. Ordinarily where remedies are possible if necessary, the employer is not required to abstain from action until everything is completed. But if the time period extends indefinitely and works a genuine hardship, you may be able to argue for some interim relief or accommodation -- assuming that the appeal process is not delayed by your request or action.
Look, with 23 years of tenured employment, you need to make a full-on no-quarter-given effort to save your employment. Get a lawyer, a good one, with demonstrated skill and experience in dealing with your specific employer. Make whatever investment required to fund this defense. This is hardball and you have a great deal at stake. Good luck to you.
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