President Obama made addressing climate change the most prominent policy vow of his second Inaugural Address, setting in motion what Democrats say will be a deliberately paced but aggressive campaign built around the use of his executive powers to sidestep Congressional opposition. “We will respond to the threat of climate change, knowing that failure to do so would betray our children and future generations,” Mr. Obama said on Monday at the start of eight sentences on the subject, more than he devoted to any other specific area. “Some may still deny the overwhelming judgment of science, but none can avoid the devastating impact of raging fires, and crippling drought, and more powerful storms.”