Republican senators headed for home Thursday with marching orders to sell their tax cut bill that takes effect next month, which came with a warning that failure to do so might mean the end of the GOP majority in the House and Senate.

"It's selling itself," said Sen. Rob Portman, R-Ohio, one of the GOP's most influential voices in favor of the bill during discussions last year. "But yeah, we need to talk about it more because we tend to move on to the next topic."

Republicans were given the jarring message Thursday in the form of a memo from the Congressional Leadership Fund, a super PAC focused on maintaining the House GOP's majority, which said the tax law is the only salvation for the GOP.

"Incumbents must begin to educate their constituents on this specific legislation and how it cuts taxes for the middle class," said Corry Bliss, CLF's executive director. "There is no positive outcome in November if we do not show that we cut taxes for the middle class and are working to make their lives better. Period."

According to the memo, CLF polled 69 congressional districts and found that the tax bill is underwater in 52 of the districts. They also found a plurality of voters in 50 districts believe the bill will raise their taxes. Despite the polling, Republicans are optimistic about the tax law's impact on the midterm elections in just over 10 months, but echo CLF's call to effectively message on the tax law.

Members believe part of the sales job is being picked up by the various companies that have announced raises and bonuses for employees thanks in part to the law. On Thursday, Portman carried around a double-sided sheet of talking points titled "Tax Reform: The Good News," listing the highest profile companies who announced similar raises and bonuses from the past week, including Home Depot, Starbucks, and Apple.

Republicans are also quick to point out the bump the tax law has seen in recent public polling, including a New York Times/Survey Monkey poll released last week showing 46 percent support the bill compared to only 37 percent in early December, just prior to the bill's passage.

And some GOP lawmakers say they have received a positive response from constituents at events back in their home states and districts. Sen. Chuck Grassley, R-Iowa, said that during his seven events in the state during the Martin Luther King Jr. holiday weekend, attendees only asked once about the bill — much less than he anticipated.

"I would expect that the way it got hammered by the Democrats prior to its passage, I would have been talking about it half of the time," Grassley said. "I'm not worried about it."

But most members still agreed they still need to message the bill to boost its popularity. A Pew Research Center survey released Wednesday shows that the bill has a plus 9 net favorability among those who understand the bill, but a minus 24 net favorability with those who do not — underscoring the need for members to sell the bill while away from Washington.

"It should be a chorus for all members coming back home and talking about the success of the tax reform efforts," said Sen. Tim Scott, R-S.C., who helped push the GOP tax bill across the finish line along with Portman and a few others. "It is a transformative piece of legislation and its success is undeniable."

"At the end of the day, the more people know about it, the more people like it," Scott added.