Raymond James analyst Pavel Molchanov noted that the California Air Resources Board aims to formalize new rules mandating fleet adoption of electric trucks in the spring of 2020, which he views as a long-term headwind for CNG fuel suppliers like Clean Energy. California is the largest U.S. market for both CNG and LNG, meaning any dropoff in demand for those fuels in the state "would have a disproportionate effect on companies such as Clean Energy," said Molchanov, who believes the market is underestimating the risk fleet electrification represents. He keeps an Underperform rating on Clean Energy shares.