By Julia Edwards Ainsley WASHINGTON (Reuters) - With a deadline looming this week to avert a U.S. government shutdown, Congress returns to work on Monday as President Donald Trump leans on Democrats to include funding for his promised border wall with Mexico in spending legislation. The Republican president took to Twitter on Sunday to warn Democrats that the Affordable Care Act, popularly known as Obamacare, could soon lose essential funding without Democratic support for a congressional spending plan to keep the government running. Should talks fail, the government would shut down on Saturday, Trump’s 100th day in office.