 -- Americans by more than a 20-point margin prefer the existing federal health care law to the latest, imperiled Republican alternative -- another challenge to the GOP’s long-held effort to repeal and replace Obamacare.

The public supports Obamacare over the proposed Graham-Cassidy bill by 56-33 percent in a new ABC News/Washington Post poll. Intensity of sentiment also is on the current law’s side: Forty-two percent strongly prefer it, nearly twice as many as strongly prefer the GOP plan.

See PDF with full results here.

The result is similar to public views on the previous GOP repeal-and-replace effort, which failed in July. Americans preferred Obamacare to that plan by 50-24 percent, again with a 20-point advantage for the current law in strong sentiment.

The latest GOP plan suffered a blow today when Sen. John McCain, R-Ariz., said he’d oppose it. His decision could be fatal to the measure, as it was in July.

Given that the bill is comparatively little-known, the survey summarized Graham-Cassidy by noting that it would end the national requirement for nearly all Americans to have health insurance, phase out the use of federal funds to help lower- and moderate-income people buy health insurance and let states replace federal rules on health care coverage with their own rules.

Notably, nearly a quarter of Republicans (23 percent) and a third of conservatives (31 percent) say they’d prefer Obamacare to this proposal.

Beyond typical political and ideological divisions, there’s a vast racial gap in this poll, produced for ABC News by Langer Research Associates. Seventy-five percent of nonwhites prefer Obamacare, compared with 45 percent of whites. Age gaps are substantial, with preference for Obamacare ranging from 63 percent of young adults to 47 percent of seniors. Preference for Obamacare ranges from 61 percent among those with household incomes less than $50,000 down to 48 percent of those with $100,000-plus incomes. And there’s a big gender gap: Sixty-two percent of women prefer Obamacare; 50 percent of men agree.

Methodology

This ABC News/Washington Post poll was conducted by landline and cellular telephone Sept. 18-21, 2017, in English and Spanish, among a random national sample of 1,002 adults. Results have a margin of sampling error of 3.5 points, including the design effect. Partisan divisions are 31-23-36 percent, Democrats-Republicans-independents.

The survey was produced for ABC News by Langer Research Associates of New York, N.Y., with sampling, data collection and tabulation by Abt Associates of Cambridge, Massachusetts. See details on the survey’s methodology here.