  Consider polynomial sequences that satisfy a first-order differential
recurrence. We prove that if the recurrence is of a special form, then the
Tur\'an expressions for the sequence are weakly Hurwitz stable (non-zero in the
open right half-plane). A special case of our theorem settles a problem
proposed by S. Fisk that the Tur\'an expressions for the univariate Bell
polynomials are weakly Hurwitz stable. We obtain related results for Chebyshev
and Hermite polynomials, and propose several extensions involving Laguerre
polynomials, Bessel polynomials, and Jensen polynomials associated to a class
of real entire functions.
