President Trump is poised in the coming days to announce his plans to dismantle the centerpiece of President Barack Obama ’s climate change legacy, while also gutting several smaller but significant policies aimed at curbing global warming. The moves are intended to send an unmistakable signal to the nation and the world that Mr. Trump intends to follow through on his campaign vows to rip apart every element of what the president has called Mr. Obama’s “stupid” policies to address climate change. The timing and exact form of the announcement remain unsettled, however.