Simple: that's not what the law says. At least not in Idaho.

According to the court's opinion, what the law says is that a trustee who forecloses must meet four specific requirements. None of those requirements equate to proving that you have "standing" (which was what Trotter alleged was required) to foreclose.

However, the first of the four requirements (p. 5 of the court's opinion) is: "The trust deed, any assignments of the trust deed by the trustee or the beneficiary and any appointment of a successor trustee are recorded in mortgage records in the counties in which the property described in the deed is situated". Since the main concern given in the article is that MERS and similar arrangements are circumventing the recording of who owns or has claims on real property in the local jurisdictions, it would appear that in the Trotter case, that concern was not present, since the relevant claim information was recorded in the local jurisdiction; the trustee who forecloses has to be the one whose trust deed is filed with the county for that property.