What is the burden of establishing prejudice against a defendant who has entered into a plea bargain?

"[T]he defendant bears the burden of establishing prejudice. [Citation.] To that end, the defendant must provide a declaration or testimony stating that he or she would not have entered into the plea bargain if properly advised. It is up to the trial court to determine whether the defendant's assertion is credible, and the court may reject an assertion that is not supported by an explanation or other corroborating circumstances." (People v. Martinez (2013) 57 Cal.4th 555, 565.)