WASHINGTON — When Denis R. McDonough, the White House chief of staff, first saw the document in a meeting in the Roosevelt Room, he immediately dispatched his aides to the West Wing basement to get copies for all of President Obama's top advisers. Royal blue and emblazoned with the White House seal, the "Official Affordable Care Act Enrollment Countdown" is a paper calendar that keeps track of the time before uninsured Americans can begin signing up for coverage under the president's signature health care law. On Tuesday, the top page said simply: "70 Days Left."