The person making a trust -- a legal vehicle to manage property -- transfers assets into it for her use during her lifetime. In the trust document she specifies beneficiaries, who are to benefit from the assets at her death. A disgruntled family member can challenge the trust, but only in special circumstances will a spouse have standing to do so.
A living trust is a legal document that creates a revocable trust to manage property. Generally, people making trusts name themselves both as the trustee, who manages the trust property, and as the beneficiary, who gets use of the property. The maker also names successor trustees to step in when the maker becomes incapacitated or dies, and successor beneficiaries to benefit from the trust property upon the maker's death. Living trust assets are not included in the probate estate but pass separately according to trust terms.
Standing to Sue
A living trust is not immune to suits from disgruntled heirs. A living trust can be challenged on many of the same grounds as a will, including fraud, incapacity and undue influence. If your spouse has evidence that he was left out of the living trust due to improper or illegal behavior, he could bring a suit. However, only the real party in interest has standing to sue. The spouse of a disgruntled heir generally won't have standing to sue in her husband's name unless she does so as his attorney or as attorney in fact of an incapacitated spouse.
Sue the Trustee, Not the Trust
If you do have standing to sue, be careful who you name as defendant. Naming the living trust as a defendant in a lawsuit is a mistake you make only once, since this kind of suit goes nowhere. Rather than naming the trust as defendant, you must bring any suit involving trust property against the trustee, who is the legal representative of the trust. If you name the trust as the defendant, the fact that the trustee is also named as an individual defendant doesn't take care of the problem; you must name her as trust representative.
Considerations When Suing
Like wills, living trusts can and often do include "no-contest" clauses. A no-contest clause is language in a trust or will that nullifies a bequest if an heir contests the document, leaving him instead a nominal sum, like one dollar. If your spouse was not named as a beneficiary of some property but was named as a beneficiary of other property, he may lose his bequest by attempting to get more. If your spouse was entirely left out of the trust, he has nothing to fear from a no-contest clause by bringing suit.