When he ran for U.S. Senate in 2014, there was nothing Bill Cassidy talked about more than consigning President Barack Obama's signature health care law to history. This was the Republican Party line at the time, and a pretty effective one, judging by the number of GOP senators who campaigned the same way on the same issue and won.

Fast forward to 2017, the Trump era and Republicans' first chance to actually make the Affordable Care Act disappear. Suddenly, individual citizens, state leaders and federal lawmakers are focusing on the prospect of taking health care away from millions of Americans. And suddenly, some members of Congress, particularly in the Senate, are balking at the prospect of actually passing a repeal/replace bill that a sitting president would sign.

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And suddenly, even Bill Cassidy is singing a somewhat different tune.

In some ways, Cassidy is well-suited to emerge as an independent voice on health care. As a longtime physician who worked in Louisiana's Charity Hospital system, he knows not just medicine but the ins and outs of providing indigent care.

In others, he's an unlikely voice of caution over efforts by the House Republicans leadership and President Donald Trump's administration to ram through a poorly received bill that Congress's own analysts say would cause some 24 million Americans to lose coverage. Cassidy basically ran for office on the promise that he'd adhere to the party line, and never suggested that health care would be an exception. He repeatedly denounced incumbent Democrat Mary Landrieu for being willing to side with Obama, and her support for the ACA was by far the highest profile example.

That was back when the discussion was academic, when Obama still sat in the White House and there was no chance the repeal drive was going anywhere.

And now that there's a real chance, Cassidy has surprisingly emerged as an independent and relatively responsible voice of prudence, and a pretty public one at that.

The first hint of a new tone came just after Trump was inaugurated, when Cassidy joined with a handful of senators in offering an amendment saying that Congress shouldn't repeal the law without offering a simultaneous replacement. The amendment never made it to a vote, but the sentiment was registered.

Now that House Speaker Paul Ryan is pushing a House GOP proposal, Cassidy, who holds seats on two of the key committees that would have to vote on the bill, has become downright outspoken.

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He was one of the few Republicans to openly admit that the Congressional Budget Office's report, which included the 24 million figure, was "awful" (Slate awarded him the tongue-in-cheek "honesty prize" for not ducking the issue, as many of his colleagues did). He told the New York Times that the time for philosophical debate is over. and it's time to be pragmatic.

“There’s a widespread recognition that the federal government, Congress, has created the right for every American to have health care,” he said. “If you want to be fiscally responsible, then coverage is better than no coverage.”

Last week he published an op-ed in "The Hill," a publication that covers Washington politics, that straightforwardly debunked three "myths": that Congress hasn't already entitled Americans to health care, citing Medicare, Medicaid and other programs as well as the law that requires emergency room to treat all comers; that cutting federal support saves society money; and that it's somehow good politics to deprive constituents — including many Trump voters — of affordable coverage.

Cassidy has actually introduced his own plan, along with U.S. Sen. Susan Collins from Maine, that would allow states to keep participating in the Affordable Care Act if they choose. And Democratic Gov. John Bel Edwards, who is pushing hard to preserve the Medicaid expansion that has provided new coverage to more than 400,000 Louisianans in its first year, says that Cassidy is in regular contact with his administration.

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Not that the senator has become a cheerleader for the ACA. He did make a disingenuous argument recently that the term "Obamacare" only applied to the unpopular parts of the law, not the parts most people support. He continues to defend the idea of spending caps for Medicaid, which would likely reduce funding in Louisiana, where some 35 percent of the population relies on the program. If the House bill came to a vote, it's not clear whether he'd actually vote no.

Still, Cassidy has emerged as one of the key voices of skepticism in the Senate. With no history of bucking the party and with no real worries about having to please voters in a closely divided state, he's surely the most unlikely one.

And face it. If the party leadership loses people like Cassidy, the Affordable Care Act is here to stay.

Follow Stephanie Grace on Twitter, @stephgracela.