The super PAC aligned with House Speaker Paul Ryan, R-Wis., is warning Republicans against complacency amid a brightening economic outlook and polls that suggest the GOP is in better shape for the midterms.

In a memorandum publicized Thursday, Congressional Leadership Fund revealed that polling in 52 of 69 potentially competitive House districts found that the Republican tax overhaul remains unpopular with voters. In 50 of those districts, a plurality of voters believe the new law will raise their taxes.

“Since the passage of tax reform, both public and private polling show signs of an improving environment — but Republicans still face a challenging environment and history suggests we should lose the House,” Corry Bliss, CLF’s executive director, said in the memo.

The tax overhaul bill in late December was approved by the Republican-controlled Congress on a party-line vote and signed by President Trump. Deeply unpopular at the time, recent national polls have shown an uptick in the law’s favorability, as major corporations have announced bonuses, raises, and planned investments in jobs and infrastructure.

Some national surveys have simultaneously revealed small but significant improvements in Trump's job approval rating and the generic ballot question that asks voters which party they would prefer be in charge on Capitol Hill. Democrats still hold a sizable lead, but their advantage has shrunk since last month.

The CLF memo, noting these developments, cautions Republicans against dismissing the threat to the party’s 24-seat House majority in the fall elections, emphasizing that voters’ views of the tax law are central to the GOP’s prospects.

“Incumbents must begin to educate their constituents on this specific legislation and how it cuts taxes for the middle class,” Bliss said.

The super PAC s investing up to $100 million this cycle on an advertising and voter turnout program to help Republicans hold competitive House seats, with plans for more than 30 field offices in targeted districts.

Aside from the tax bill, the memo claims that House Minority Leader Nancy Pelosi's toxicity will help keep wavering Republican voters in the fold in November. Left unsaid in the memo is that Republican operatives believe the California Democrat's unpopularity will help counteract Trump, who is an anchor on GOP candidates in many battleground seats.

Also unmentioned are claims by many House Republicans that an FBI conspiracy tried to take down Trump — before the 2016 presidential election and after. The topic has become a major focus of congressional Republicans in media interviews and other forums. To win in 2018, they might better serve themselves by keeping the spotlight on the tax bill.

“Members need to identify the 50,000 voters they need to win and communicate with them as often as possible about what they are doing for their communities,” Bliss said.