4 5 1 4 1 2 1 . Colleen Doering runs tax implications of buying into a business small facilities maintenance business in Florida. The tax overhaul that President Trump signed into law now has more supporters than opponents, buoying Republican hopes for this year’s congressional elections.

The growing public support for the law coincides with an eroding Democratic lead when voters are asked which party they would like to see control Congress. And it follows an aggressive effort by Republicans, backed by millions of dollars of advertising from conservative groups, to persuade voters of the law’s benefits. That campaign has rallied support from Republicans, in particular. But in contrast with many other issues — including Mr. Trump’s job approval rating — it also appears to be winning over some Democrats.

Support for the law remains low among Democrats, but it has doubled over the past two months and is twice as strong as their approval of Mr. Erin Parker, a high school history teacher in San Antonio, said she did not like many elements of the law, particularly its big reduction of the estate tax, and said she was skeptical that it would provide much of an economic lift. Parker, who described herself as an independent who tends to support Democrats, said the bill would probably help the technology start-up where her husband works. Over all, 51 percent of Americans approve of the tax law, while 46 percent disapprove, according to a poll for The New York Times conducted between Feb. Considering where it was, it is dramatically different.

Cohen cautioned that the bill still was not particularly popular, and opposition among Democrats remained strong. Still, support has grown even among Democrats, from 8 percent just before the bill passed in December to 19 percent this month. Cohen said, running on opposition to the bill has become more of a political gamble. This isn’t a problem yet for Democrats, but the movement isn’t a positive one. Other recent polls have shown similar upswings for the law, including a Monmouth University Poll in late January that found support for it had risen to 44 percent nationally, from 26 percent in December. Lori Weigel, a partner with Public Opinion Strategies, a Republican polling firm. That is certainly in part due to consistent communications about the tax plan and the news coverage of prominent companies investing in workers.

Democrats have done little to counter the Republican messaging and concede it has had an effect, along with a series of high-profile company announcements of bonuses, raises or other benefits attributed to tax savings. But they are ramping up efforts to rebrand the law as disproportionately helping shareholders and the wealthy, and they contend the boost from bonus announcements will fade. Nicole Gill, executive director of Tax March, a liberal group that has organized rallies and protests against the new law. The fundamentals of the bill remain the same. The bill that passed is the bill that polled at 35 percent in December, and Democrats should keep talking about that.

President Trump signing the tax bill in December. Support for the law — though not for Mr. Trump himself — is growing even among Democrats. The Times polling suggests that Americans are overestimating the degree to which the benefits of the law’s corporate tax cuts are flowing straight to workers — while underestimating the likelihood that the law will reduce their individual taxes. Just under one in five respondents expect to see either a raise or a bonus thanks to the law’s business tax cuts. Early returns from public companies indicate that’s an overshot. Martin Whittaker, Just Capital’s chief executive.

Only one in three respondents expects to receive a tax cut from the law. Republicans are confident that support will continue to grow as more Americans see lower taxes reflected in their paychecks. Close to half of Americans now expect some direct benefit from the law — either a tax cut or a salary increase or bonus. Support for the bill is far stronger among that group: More than three-quarters of Americans approve of the law, compared with fewer than a third who don’t expect a benefit or aren’t sure. Gina Coats, a project manager for a plumbing company in Springfield, Mo. It’s causing people to let go of their money a little more easily.