There are a lot of reasons Americans might be skeptical of the Republican-backed tax bill — which, poll after poll after poll tells us, they are.

One reason they might be skeptical is they understand how the benefits of the bill are weighted: heavily toward wealthier Americans and businesses. Analysis from the Tax Policy Center shows those in the top 5 percent of U.S. households will see much larger benefits next year than will everyone else and once the income-tax cuts expire (while the business cuts remain) the only significant benefits will be seen by the top 1 percent of Americans.

Another reason may be that the Republican arguments in defense of the bill have often been a bit muddied, or, as the bill has evolved and mutated, those arguments have been clipped away. Once upon a time, House Speaker Paul D. Ryan (R-Wis.) promised fewer tax brackets and a return that could be filed on a postcard. So much for that.

The most recent example of questionable messaging came on Twitter from Senate Majority Whip John Cornyn (R-Tex.).

“Under this very specific and hard-to-understand scenario that includes weird and seemingly contradictory descriptors with which many Americans are not familiar, this bill is good.” And yet, with rhetoric like that, recent polling has the legislation languishing at around 30 percent! A true mystery.

The tax bill is so unpopular it has consistently polled below one of the least popular figures in American politics: President Trump, the man who will probably sign it into law. On Tuesday, CNN released a poll in conjunction with its polling partner SRSS that had the tax bill at 33 percent support and Trump at 35 percent. Neither of those numbers is the sort of thing most politicians would embrace as positives.

There is another aspect to those poll numbers that is worth pointing out. In two recent polls, CNN’s and one from USA Today and Suffolk University, there has been a strong connection between those who like Trump and those who like the tax proposal. Among those with an opinion about the tax bill, about 9 in 10 of those who approved of Trump’s job performance in CNN’s poll also liked the legislation and about 9 in 10 of those who disapproved of him disliked it. In the Suffolk poll, a similar effect. (Many people had no opinion on the legislation, perhaps because they were unfamiliar with it; the percentages below include that group.)

This is, perhaps, a key reason people are skeptical of the bill: Many of them are also skeptical of Trump. Those polls above suggest — though they don’t prove — views of the tax bill are inextricable from views of the president. Some people like one and not the other, yes, but only a small percentage. For everyone else, preferences align. You like Trump, you like the bill; you don’t, you don’t.

Part of this is a function of who likes both of these things. Republicans overwhelmingly like both Trump and the tax plan, so they account for a lot of those bubbles. (Democrats dislike both, as you might expect.) The effect is broader than that. When The Post and our partners at ABC News polled on the legislation last month, only about half of those who said they approved of the tax bill were Republicans. A third were independents. This isn’t just about party.

(Our poll had the same splits as above: Of those with an opinion, 9 in 10 liked both or disliked both.)

To some extent, this is good news for the Republican Party. If many of those who oppose the legislation now do so because Trump supports it (which, again, we can’t quantify precisely based on the numbers we have at hand), it suggests that, should people start to see positive effects from the still-theoretical bill, their opinions of it — and the party that passed it — might improve. Once it exists by itself, that is, it can be evaluated outside of the president who advocated it.

For the moment, though, it is a reminder of the problem for Republicans on Capitol Hill. Their own voters approve of them and the president, a boon for those seeking reelection next year. Many other Americans, though, see their actions through the lens of a president they vehemently dislike, suggesting even well-meaning legislation could face opposition solely because of the president who advocates it.

This may not be such legislation, and Americans clearly don’t see it as such. Republicans just have to hope it can eventually have room to grow out of Trump’s shadow. And that it finally earns the approval of those Americans with both business income and income from noncorporate businesses who are married filing jointly — or whatever it was.