WASHINGTON (AP) — President Joe Biden faces a steep path to achieve his ambitious goal of slashing planet-warming greenhouse gas emissions in half by 2030. His $2 trillion Build Back Better plan contains $550 billion in spending and tax credits aimed at promoting clean energy. But it was sidetracked by Democratic Sen. Joe Manchin, who said just before Christmas that he could not support the legislation as written. Even without the legislation, Biden can pursue his climate agenda through rules and regulations. But those can be undone by subsequent presidents, as demonstrated by Biden reversing Trump administration rules that rolled back protections put into place under Barack Obama.