WASHINGTON — President Trump is about to score a big win, but not the kind he promised.

The luxury hotel builder who campaigned as a champion of the "forgotten" middle class is poised this week to sign his first major bill — a tax overhaul that could deliver its biggest benefits to the wealthy and big corporations.

The middle class, too, is expected to receive a tax cut under the plan that House and Senate Republicans are slated to give final approval Wednesday morning — but unlike the corporate provisions, their breaks are temporary and add up to much less than those millionaires would enjoy.

Yet Trump is eager for a win — and so are congressional Republicans, who are facing a potential electoral buzzsaw in the suburbs next year, and are desperate to rally their base and donors with a signature achievement.

So GOP lawmakers, including those from the battleground Philadelphia suburbs, have hitched their fortunes to the tax measure, hoping that its reality turns out more rosy than most analysts and voters expect.

Every House Republican from outside Philadelphia, except for Rep. Frank LoBiondo, a New Jerseyan who is retiring, supports the measure, and Sen. Pat Toomey (R., Pa.), has been one of its most vocal advocates.

Polls, however, say that the public doesn't believe the bill will help working families.

"They're starting out with the most negative reaction to any tax bill in the past couple of generations," said Patrick Murray, director of the Monmouth University Polling Institute, which found that 47 percent of the public opposes the bill while 26 percent supports it.

Two tax increases have even polled better. Said Murray, "That's a big hole to dig out of."

Similarly, an NBC/Wall Street Journal poll released Tuesday found that 63 percent of Americans think the tax plan will mostly help corporations and the wealthy, against 22 percent who believe it was designed to help everyone.

Republicans argue that the bill has been victimized by exaggerated liberal critiques and a compliant media, and that people will warm up to the measure once they start seeing more money in their paychecks next year (though most won't see the full effects until they fill out their taxes in 2019, after next year's midterm elections).

"If you look at the actual facts that are in the bill, there's going to be a lot of economic growth, wages are going to be lifted, I think the stock market has already responded," said Rep. Ryan Costello (R., Pa.), one of the region's most vulnerable incumbents. Over time, "people will see the positive benefit of it."

A family of four with $80,000 income, he said, could see a $2,000 tax cut. That could be the difference between taking a family vacation or not, buying a new car, extra Christmas presents, or more nights out to eat, he said.

Republicans also argue that future Congresses will extend individual tax breaks, much as lawmakers did for nearly all of the tax cuts passed under President George W. Bush. That would add benefits to the middle class that aren't being counted now, but also spike the bill's price tag.

"I know people are going to see dramatic improvements that are going to change their view of this," said Rep. Tom MacArthur (R., N.J.).

He is the only lawmaker from New Jersey backing the bill. Every other one criticized a new $10,000 cap on the deduction for state and local taxes — a provision that could also hit some homeowners in Philadelphia's western suburbs who pay high property taxes and the city's wage tax.

Voters are more pessimistic than even the most critical tax analysts.

For example, while the nonpartisan Tax Policy Center projects that 80 percent of taxpayers will get a cut next year, the Monmouth poll found that 55 percent of those making less than $50,000 expect to pay more.

The dour expectation likely reflects a perception among middle-class families that the tax bill is not for them.

"This is a tax cut in the short run for the middle class, but it's not nearly as big of a tax cut as it is for corporations, small business owners or the very wealthy," said J. Richard Harvey, a former senior accountant in the Reagan administration's Treasury Department who now teaches at Villanova's Charles Widger School of Law.

Added Joel Slemrod, who worked as an analyst for President Ronald Reagan's Council of Economic Advisers and now teaches economics at the University of Michigan, "Any tax cut aimed at business income, as opposed to employee income, is going to tend to be skewed toward high-income people."

To be sure, there is help for the middle class, at least initially. The Tax Policy Center predicted that people making between $49,000 and $86,000 a year would get a tax cut averaging $930 next year. But by 2027 they'd pay a little more, on average, than they do now. Several other analyses, including from the Penn Wharton Budget Model, projected broadly similar results.

A key question is if that $930 is enough to make them fans of the bill. Former President Barack Obama enacted a payroll tax cut worth a similar amount — but few people noticed, Murray said.

Meanwhile, people in the top 20 percent would get a $7,460 tax cut next year, the Tax Policy Center found.

Democrats also blasted the bill for including a repeal of the Affordable Care Act mandate that everyone carry health insurance — a move that Republicans say will free people to make their own health decisions, but that nonpartisan congressional analysts say will raise insurance prices and lead to 13 million fewer people having health care by 2027.

Still, the measure will give Trump support for his boasts of monumental achievement in his first year. And his fellow Republicans have long supported tax cuts — and now see the bill as a way to show they have done something for their supporters.

"If you go into the election year and you don't have any big legislative wins," said Jim Gerlach, a former Republican congressman from Chester County, "then the body of the electorate is going to say, 'We put you in charge and you didn't get stuff done, so why should we keep you in charge?'"