WASHINGTON A crush of sign-ups expected Tuesday on the last day of open enrollment for HealthCare.gov could help solidify the standing of “Obamacare” as an improbable survivor in the Donald Trump years. In 36 states that use HealthCare.gov,- Dec. 15 is deadline day for coverage that starts Jan. 1, while another 14 states and Washington, D.C., have later dates. Analysts and advocates who follow the annual insurance sign-ups say interest has gotten stronger with the coronavirus pandemic gripping the nation. Also, the legal cloud hanging over the Affordable Care Act seemed to start lifting last month when Supreme Court justices gave a skeptical reception to the latest challenge from the Trump administration and conservative-led states seeking to overturn the law in its entirety.