The statement suggests that Vietnam is facing increasingly complex and difficult policy challenges. "Navigating" means managing or dealing with these challenges, implying that Vietnam is trying to find appropriate solutions or approaches. The word "steadily" implies that the challenges are progressively becoming more difficult over time. The word "thornier" suggests that these challenges are becoming more intricate, complicated, or problematic. Overall, the statement highlights the increasing complexity and difficulty Vietnam is facing in its policy decision-making.
