Republican Donald Trump's presidential election victory all but dooms major Obama administration initiatives that are already tied up in legal challenges and gives him the chance to appoint a pivotal fifth conservative justice on the U.S. Supreme Court.

Democratic President Barack Obama's signature 2010 health care law, his plan to combat climate change, his executive action on immigration, his transgender rights policy and other issues were challenged in court by Republicans and industry groups.

A Trump administration could decide no longer to defend the policies in court after Trump takes office on Jan. 20. In addition, Trump and the incoming Republican-led Congress could simply repeal or rescind Obama's policies, as they have promised.