Steven Dennis of Bloomberg Businessweek explains why a freshman Southern senator could play an important role in the weeks ahead.

Bill Cassidy, the first-term Republican senator from Louisiana, thinks the House’s Obamacare repeal bill failed to consider the impact it will have on one crucial constituency: patients. A medical doctor whose political life was forged in the aftermath of Hurricane Katrina and during decades working in a charity hospital, Cassidy wants a more robust replacement for Obamacare, one that lives up to Donald Trump’s campaign promise to replace it with a law that covers more people at a lower cost.

That might sound like wishful thinking, yet if Senate Republicans want to do anything on health care, they have no choice but to listen to Cassidy. Although he wasn’t included in the 13-member working group tasked with crafting a Senate bill, Cassidy has emerged as perhaps the most critical vote—the elusive Republican who can make or break Trump’s top legislative priority.

With 52 seats in the Senate, the GOP can afford to lose just two of its own and still pass a bill without Democratic support. Given conservative insistence on defunding Planned Parenthood as part of the effort, Republicans could, for instance, lose the support of moderates Susan Collins of Maine and Lisa Murkowski of Alaska. That would set up a scenario where Cassidy becomes the decisive vote and Vice President Mike Pence casts a tiebreaking 51st vote, with Democrats powerless to filibuster under special budget reconciliation rules.

Cassidy wants a bill that lowers premiums and expands coverage, and says the American Health Care Act passed by the House fails to deliver.

Patient-centered health care reform? Where have we heard that before?