What is the burden of proving the constitutional validity of a prior conviction?

Although Ebner apparently stood for the proposition that on an appeal it is the burden of the People of prove the constitutional validity of a prior conviction, this did not remain the law. In People v. Merriam, 66 Cal.2d 390, 58 Cal.Rptr. 1, 426 P.2d 161, where the matter was thoroughly discussed, it was held that the validity of prior convictions was not reviewable where they are 'sought to be challenged for the first time on direct appeal from the judgment wherein such prior was found to be true * * *' ⁵ (66 Cal.2d at 396, 58 Cal.Rptr. at 5, 426 P.2d at 165.) The reason for the Merriam rule is obvious: if the validity of a prior conviction is challenged in the trial court, the People have an opportunity to make the silent record speak. ⁶ The same is true where the assault takes the form of a habeas [268 Cal.App.2d 768] corpus petition. Again the People have notice of the claim and are given a chance to overcome the presumptions that favor the defendant. The People's right to attempt to do so can only be satisfied by a candid challenge at the trial level. Obviously an appellate ambush will not do. ⁷