Possibly. It depends on what the POA says. But before even trying to do this, I would meet with your attorney and determine whether this is the best thing to do. I am not sure why you would want to do so, offhand.
If the POA does not allow you to revoke the trust, I would assume that you are also named as Trustee, or successor trustee, of the trust. In that position, you have a great deal of control over what happens with the trust assets, subject of course, to whatever provisions or restrictions the trust dictates.
You should get legal advice before doing anything, at this point.
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I send you my sympathy that you and your husband face this current challenge. I agree with the prior responder that it is important to review both the power of attorney and the trust document with an experienced attorney so that you'll be able to come up with a course of action in the best interests of your husband. If you were named as the successor trustee/co-trustee and/or agent you do have certain rights and fiduciary responsibilities with which to comply. You would want to consider all of your options so that you may make an educated decision. Incompetency and death are usually times when an revocable trust becomes irrevocable and there are not enough facts known to make a determination.