Several surveys show approval of the law falling after increasing earlier in the year, following favorable coverage about companies using their corporate tax-cut windfalls to give raises and bonuses to workers. But those gains have since faded and Democrats have continued to hammer what they deride as a "Republican tax scam" that has disproportionately benefited executives and wealthy Americans.

Perceptions of the tax law aren’t positive even in Republican-dominated states -- a Quinnipiac poll of Texas voters taken in April found that 43 percent of voters there approved while 45 percent disapproved of the law.

‘Hurricane of Issues’

Republican strategists who had hoped to focus their fall campaigns on the tax law are having second thoughts. One firm seeking to protect the party’s congressional majorities has seen a drop-off in the effectiveness of its ads touting the overhaul and is mulling a pivot to other issues amid doubts in the tax law’s ability to persuade or mobilize voters to back GOP candidates, according to a person familiar with the matter who was granted anonymity to discuss it.

“It’s not hard to run on taxes so long as the economy is doing well,” said Jason Fichtner, senior research fellow at the Mercatus Center at George Mason University. “But it’s hard to go out and talk about tax law changes when it’s drowned out by trade, immigration, detainments, malfeasance and potential abuses of power by officials.”

After trying different messaging tactics -- such as the tax law leading to tax hikes -- Democrats are now focused on Congressional Budget Office projections showing the law’s provision to scrap the Obamacare individual mandate tax penalty is causing higher health-care costs.

While taxes ranks low on the issues motivating voters, several recent surveys have found that health care is the top issue for Americans nationally.

Debbie Mucarsel-Powell, the Democrat facing Curbelo in one of the most competitive races, released a statement Wednesday blasting the Republican for having voted for Trump’s "massive tax cut for corporations that will line the pockets of the wealthiest Americans, including his family and donors, and will raise health-care premiums for families everywhere."

Republicans are hoping to revitalize interest in taxes by introducing legislation that would extend the tax cuts for individuals and streamline tax-favored retirement and education savings accounts.

“There are a hurricane of issues right now in Washington, which makes it harder,” said House Ways and Means Chairman Kevin Brady, a Texas Republican. “I know this, if tax reform weren’t working there would be plenty of coverage of it. Every indicator is better than before.’”