President Barack Obama is traveling to Capitol Hill on Saturday to try to close the sale on his signature health care overhaul, facing a make-or-break vote in the House certain to be seen as a test of his presidency.Obama scheduled a late-morning visit with House Democrats convening a rare Saturday session on legislation to remake the U.S. health care system, extending coverage to tens of millions now uninsured and banning insurance company practices such as denial of coverage based on pre-existing medical problems.