Many lawyers advise their clients that trusts are harder to contest than wills. This assertion is simply not true. There is a large body of law regarding will contests with which lawyers are very familiar. They are less familiar with the body of law that pertains to trust contests.
Arizona has case law that governs many important aspects of trust contests. Arizona appellate courts have ruled that where there is no controlling case law, the court will give great weight to the Restatement of the Law concerning trusts. The Restatement is prepared by distinguished scholars who are members of the American Law Institute. A very comprehensive Third Restatement of the Law of Trusts was published in 2003.
The Third Restatement takes the position that trusts are often "will substitutes" and that they should be treated very similarly to wills in many respects. It goes on to explain that even though two witnesses are not needed to validly execute a trust, the same law that governs will interpretation of the wording in wills governs questions of trust interpretation.
And, just like wills, trusts can be struck down if they were the result of undue influence of another or if they were made by a person who lacked sufficient mental capacity to sign a trust.
A trust is more vulnerable than a will to challenge in the following respect: Usually trusts specify the method for their amendment. If the trustor does not follow the rules that he himself established for the amendment of his trust, the amendment will fail.
A trust is less vulnerable to challenge than a will in the following respect: Under Arizona law, when a person makes a trust, he can specify the beneficiaries of the trust. Those who are not beneficiaries have no right to see a copy of the trust. By contrast, all persons who are heirs as well as all persons who are named in a will have the right to see the will before it is irrevocably admitted to probate.