What's the most effective climate policy a single state can implement?

Climate change demands federal action, but states are acting first — and sometimes more ambitiously than Washington. California's vehicle emissions standards are now the de facto national standard. New York's building codes are reshaping construction. Texas produces more wind power than most countries. What can ONE state actually accomplish on its own? The levers available: vehicle standards, building codes, renewable portfolio standards, electric grid planning, zoning reform (to reduce sprawl), agricultural policy, and procurement. The hardest part isn't technology — it's political economy. Building codes anger contractors. Vehicle standards anger OEMs. Zoning reform angers homeowners. The politicians who push hardest on climate often get recalled or voted out. If you were advising a governor in a mid-sized state with modest majorities, which policy would you prioritize for maximum emissions impact per dollar spent? What's the most leverage available before federal coordination arrives?