WASHINGTON — President Biden has a two-step strategy to cut tailpipe emissions, the nation’s largest source of greenhouse gases: First, restore the standards to roughly the level set by President Barack Obama. Then, tighten them even further, with an aim of making the electric car the dominant vehicle sold in the United States. The Biden administration plans this month to propose a tailpipe emissions rule that would largely mimic the Obama standards, which were jettisoned in 2019 by President Donald J. Trump.