The Republican tax bill is facing its first huge test at the ballot box in Tuesday's special election for Pennsylvania's 18th Congressional District.

President Donald Trump and Republican candidate Rick Saccone have praised the legislation to voters in the district.

Democrats are going on an all out assault against the legislation.

PITTSBURGH — The massive Republican tax code overhaul passed into law late last year is facing voters in a major election for the first time Tuesday. And the law may not be going over as well as GOP leaders had hoped.

After initially launching a barrage of ads targeting Democratic candidate Conor Lamb's opposition to the GOP tax law, Republican outside groups have taken a step back on their tax messaging, instead focusing on other issues such as immigration, House Minority Leader Nancy Pelosi, and Lamb's career as a federal prosecutor.

Likely Republican voters in the district, to the tune of roughly 80%, support the tax plan, a recent Gravis survey found. But overall, just 48% of likely voters in the district approve of the law, though more likely voters approve than disapprove (36%).

Still, Democrats view the change of tune on the tax law as a sign that it isn't going over as well in the district as the GOP anticipated. In 2016, Trump won the district by 20 points.

"The observation there that's been interesting especially when it comes to the tax debate in the country is Republicans were sending millions of dollars attacking Conor Lamb on this tax package and his tax message," Democratic Rep. Ben Ray Lujan of New Mexico, chair of the Democratic Congressional Campaign Committee, told CBS News. "And for whatever reason, Republicans pulled all of that traffic this last week and now they're just assaulting him with every character assassination they can throw at the wall to see what sticks."

During rallies last week for Lamb, former Vice President Joe Biden lambasted the tax law, saying Republicans want to pay for the legislation with cuts to Medicare, Medicaid, and Social Security, drawing condemnation from rally-goers.

Joe Biden. AP Photo/Gene J. Puskar "If we do nothing in terms of cutting programs, if we just keep things as they are, America's gonna go flat bankrupt over the next 10 years. Not a joke," Biden said. "It's because this tax cut is not paid for. But they have a way to pay for it. And [Lamb's] gonna get in their way, they're afraid."

In the campaign's closing days, the liberal Not One Penny group, which is opposed to the tax plan, bought $100,000 worth of anti-tax bill ads on radio stations in the district.

Meanwhile, President Donald Trump and Saccone have both used the tax plan heavily in their messaging to voters in the district.

"We need our Congressman Saccone, we have to have him. … We need him, we need Republicans, otherwise they’re going to take away your tax cuts," Trump said during a campaign rally just outside of Pittsburgh on Saturday.

'I don't know anybody who got any raises'

Voters in the district expressed mixed feelings on the law to Business Insider. Justin DePlato, a political science professor at Robert Morris University and a delegate to the 2016 Republican National Convention representing the 18th district, said voters in the area "are very happy" with the legislation.

But Al Quaye, a Republican from the district who sought to be a delegate to the 2016 convention, said it's "too early" for anyone to have experienced gains from the bill. He said, however, that proof the legislation was a good idea can be found in stock market gains since Trump signed it.

Some Democrats said they saw small gains in their take-home pay, but nothing substantial. And they were concerned about how the legislation would later be paid for.

"I saw a small improvement, I think I got like $90 more in my pay," Mary Ann Cupples Wisniowski, chair of the Collier Democratic Committee in Pennsylvania, told Business Insider ahead of a rally for Lamb. "But what I'm worried about is when they expire. All of a sudden you'll have this big balloon payment because they're taking less out of your taxes now and if they don't increase it, I'm worried."

"Some people have said to me, 'Don't you see on TV that people are buying houses and cars?'" she said. "I said, 'I got $90. You can't buy a house or a car for $90.'"

Others echoed Wisniowski's concerns. Lynn Heckman, a member of the same committee, called the bill "a crime," adding that it has not yet effected her retirement pension. Ronald Eiben, a union carpenter attending the rally from Canonsburg, Pennsylvania, said he's noticed "very little" benefit in his paycheck. Neither did Walt Kerin, a union carpenter in attendance at the rally.

"I don't know anybody who got any bonuses," he said. "I don't know anybody who got any raises. Nothing like that."