A new survey by Priorities USA, a Democratic advocacy group, shows the approval ratings of Republican lawmakers tumble when voters hear about the details of the GOP tax plan.

The poll of more than 12,000 voters in 20 House districts and Nevada, a Senate battleground, showed that approval ratings dropped by an average of three points after voters were exposed to a $2 million digital advertising campaign against the tax bill.

Priorities USA, a group classified under section 501(c)4 of the tax code, announced its nationwide ad campaign last month.

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“The results have been striking: after voters are exposed to ads about the tax plan, the job approval numbers for the incumbent drops, and voters are more inclined to vote against the incumbent in next year’s midterm elections,” Guy Cecil, the chairman of the group, wrote in a Dec. 15 memo.

The ad campaign has also run in Maine, the home state of Sen. Susan Collins Susan Margaret CollinsClub for Growth to spend million in ads for Trump Supreme Court nominee Maryland's GOP governor says Republicans shouldn't rush SCOTUS vote before election The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November MORE (R), a key swing vote, but the recent poll did not gauge the public reaction there.

One representative advertisement urges voters to call Rep. Ryan Costello Ryan Anthony CostellloTrump struggles to stay on script, frustrating GOP again Bottom line Former GOP Rep. Costello launches lobbying shop MORE (R-Pa.) about his vote for the tax bill, which it says will give a tax cut to a well-groomed billionaire floating in a pool and pay for it by cutting the Medicare benefits of a senior woman.

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellFEC flags McConnell campaign over suspected accounting errors Poll: 59 percent think president elected in November should name next Supreme Court justice Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE (R-Ky.) has promised Collins that he will not allow a $25 billion cut to Medicare required by “pay as you go” rules that are supposed to kick in automatically if the tax bill passes.

But Democrats are pointing to a recent statement by Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.) that Congress will tackle the growing costs of programs such as Medicare, Medicaid and welfare next year.

The survey, by Bully Pulpit Interactive, the digital advertising firm that placed the ads, also showed the campaign increased the Democratic advantage on the generic ballot.

A November survey by Priorities USA showed Democrats leading Republicans by 11 points, 45 percent to 34 percent. But after being exposed to the messaging campaign, the Democratic advantage grew to 17 points, 50 percent to 33 percent.

Ads highlighting the potential impact of the tax bill on Medicare were most effective with men, middle-aged voters and seniors, whose approval of their representative or senator dropped by double digits after being exposed to the Democratic argument.

“This is destined to be a defining issue in House and Senate races across the country,” Cecil wrote, urging opponents of the tax bill to “not relent in emphasizing the horrible impacts.”

The unpopularity of the tax plan has surfaced in other polling.

A Marist survey released this week showed that 52 percent of respondents said the GOP plan would likely hurt them and their families, while only 30 percent thought it would help them.

Republican lawmakers on Capitol Hill say they have been focused on hammering out the details of the legislation and predict its popularity will improve once they focus more of their time and attention touting its benefits.

Several Republican senators acknowledged last week they need to do a better job of selling it.