What is the test for determining whether a defendant has a right to exercise free speech?

We "engage[ ] in a two-step process, determining first whether the defendant made a threshold showing that the challenged cause of action is one arising out of acts done in furtherance of the defendant's exercise of a right to petition or free speech under the United States or California Constitution in connection with a public issue, as defined in the statute; and if so, whether the plaintiff has demonstrated a probability of prevailing on the claim." (Jespersen v. Zubiate-Beauchamp (2003) 114 Cal.App.4th 624, 628.)