Senate Democrats might not be able to stop Republicans from tearing up President Barack Obama’s signature health care law, but they were seeking late Wednesday to make it as uncomfortable as possible. Taking advantage of an arcane Senate tradition known as a “vote-a-rama,” party leaders were prepared to go late into the night to force Republicans to take votes on popular provisions of the 2010 Affordable Care Act, warning that the party could spark chaos by repealing the legislation that has extended health insurance to millions.