P sues D for damages arising out of a two-car collision. P calls W, a witness, who observed the accident after having escaped from a mental institution to which he had been committed as a manic-depressive psychotic. At the time of trial, W has been recaptured and is back at the institution. D objects to W as a witness on the ground that W's commitment to a mental institution renders him incompetent to testify under state law (which follows exactly the federal rules). The court should: