The feasibility of implementing climate policies relies on citizen support. While recent efforts have focused on shifting the attitudes of policy opponents, little is known about the middle group who neither reflexively endorse nor reject mitigation measures. Here, using a survey of climate policy preferences across 13 EU countries (n = 19,328) in 2024, we identify the ‘conditionals’—a crucial faction of moderates whose support shifts across 15 climate measures— and examine the factors influencing their choices and quantify their electoral impact. Conditionals constitute 33% of Europeans who are active voters for the dominant centrist and centre-right parties. The preferences of conditionals hinge upon specific policy instruments and the perceived cost–benefit balances but less on fixed ideology or demographics. The potential shift of conditionals plays a vital role in shaping overall patterns of public policy support and electoral outcomes. Our findings emphasize the visible benefits of strategic engagement with conditionals for climate policy success.