While no polling system is infallible, our M.R.P. model combines respondents’ demographic characteristics, their state and their views of the A.H.C.A. to estimate the probability that a voter of a certain age, race and gender, and in a state with certain characteristics, would support the proposal. It then estimates support for the bill within every state based on each state’s demographics. Models like this have been used to accurately predict public opinion in states on other topics, and in last week’s election in Britain.

We found that Republicans have produced a rare unity among red and blue states: opposition to the A.H.C.A.

For example, even in the most supportive state, deep-red Oklahoma, we estimate that only about 38 percent of voters appear to support the law versus 45 percent who oppose. (Another 17 percent of Oklahomans say they have no opinion.) Across all the states that voted for President Trump last year, we estimate that support for the A.H.C.A. is rarely over 35 percent. A majority of Republican senators currently represent states where less than a third of the public supports the A.H.C.A. By comparison, President Trump received 33 percent of the vote in Massachusetts.

How many senators might lose their seats as a result of supporting the bill? A recent study found that Democrats who supported Obamacare lost about six percentage points in the vote in 2010 — a dangerous omen for the 15 sitting Republican senators who won their most recent elections by less than that number. For example, if the A.H.C.A. costs Republicans as much support as Obamacare cost Democrats, senators like Jeff Flake of Arizona and Dean Heller of Nevada might be in danger of losing their seats. We estimate that only 28 percent of the public in Nevada supports the A.H.C.A., while only 31 percent of Arizonans support it.

With this said, it’s hard to know just how politically damaging supporting the A.H.C.A. would be. On the one hand, no major bill this unpopular has passed in decades, but some voters might forget about the A.H.C.A., or change their opinions, by the time some senators face re-election.