WASHINGTON (Reuters) - Right after Republicans in the U.S. Senate passed their income tax overhaul in December, delivering tax cuts to businesses and most American taxpayers, Senate Republican leader Mitch McConnell was buoyant.

Surrounded by jubilant fellow Republicans, he told reporters, “If we can’t sell this to the American people, we ought to go into another line of work.”

Four months later, McConnell’s attempt at levity could prove prophetic.

The most vulnerable Republican incumbents in the tightest congressional races in the November elections are talking less and less about the tax cuts on Twitter and Facebook, on their campaign and congressional websites and in digital ads, the vital tools of a modern election campaign, a Reuters analysis of their online utterances shows.

All told, the number of tax messages has fallen by 44 percent since January. For several congressmen in tough reelection fights, Steve Knight in California, Jason Lewis in Minnesota, and Don Bacon in Nebraska, messaging is down much more - as much as 72 percent.

Right after the tax law passed, lawmakers piggybacked on a surge of corporate announcements of tax-cut fueled bonuses to employees, wage hikes and job creation plans to tout the benefits of the bill to voters.

As those corporate announcements trailed off in March and April, so did Republican politicians’ messages about tax relief, the Reuters review found. With the exception of a flurry of news releases on or around April 17, when federal tax returns were due, few incumbents kept up the pace. The Reuters review did not capture candidates’ email, direct mail or private conversations with donors or voters or stump speeches.

Most of the 13 Republican incumbents in the most competitive reelection bids, and their aides, declined to answer Reuters’ questions on why they were communicating less online about the tax cuts. But a Reuters/Ipsos poll conducted from March 14 to 29 found that just 3 percent of American adults were aware of receiving a material benefit from the Republican legislation.

Ford O’Connell, a Republican strategist, said that is why his party’s candidates need to energize voters by talking about other issues, too, like restricting immigration and stopping Democrats from taking control of the House of Representatives so that they cannot impeach President Donald Trump.

Jesse Hunt, a spokesman for the National Republican Congressional Committee, acknowledged there “has been a downtick in what voters are hearing from members and businesses on the tax reform front.” He said it was because lawmakers had moved on to other issues.

FILE PHOTO: U.S. President Donald Trump gives remarks on tax cuts for American workers as Richard Kerzetski of Universal Plumbing, North Las Vegas, Nevada, listens during an event in the White House Rose Garden in Washington, U.S., April 12, 2018. REUTERS/Kevin Lamarque/File Photo

“Candidates and members need to make sure that they stay focused on what is our signature achievement in this Congress,” Hunt said.

Five of the 13 candidates who did respond to Reuters said they do talk regularly to voters at events.

The Republican tax law sharply cut the corporate tax rate, encouraged corporations to repatriate overseas income at lower rates, and at least temporarily, cut taxes for the wealthy and most other Americans. Many of the benefits to individuals won’t become obvious until they file their tax returns in early 2019, and that is long after the congressional elections.

KOCH SPENDING

The election cycle is still in its early stage, so the volume of talk on the tax overhaul could always increase. And even if politicians are reluctant to tout it, conservative financial supporters are showing an eagerness to fill the gap. Billionaires Charles and David Koch are spending $20 million to promote the benefits of the tax cuts in battleground states with digital ads and even door-to-door canvassing.

Some polling results suggest that taxes are not the burning issue for voters that Republicans hoped they would be. A Quinnipiac University poll released in March said only 8 percent of voters thought taxes was the most important issue in deciding how to vote in the congressional elections. It was fifth, behind healthcare, the economy, gun policy and immigration.

It is also harder for Republicans to talk about lower taxes in states with high local taxes like New Jersey, New York, Pennsylvania and Virginia. That also happens to be where 10 of the 17 most competitive congressional races are.

Many taxpayers in those states will pay more in federal taxes because the new law reduces the deduction for state and local tax payments. About one in four Americans expect their state and local income taxes to rise because of the Republican tax law, while only 11 percent expect them to fall, according to a recent Reuters/Ipsos poll.

WHAT THEY DO SAY

Barbara Comstock, locked in a tight race for reelection in Virginia’s 10th Congressional District, says she talks about the tax overhaul at campaign events.

The Reuters analysis shows that though she mentioned the benefits of the tax cuts 36 times in January in social media, she did so only 13 times in March and then 22 times in April. She said in an interview that she is reacting to constituents, whose interests have moved on to other issues.

Don Bacon, of Nebraska’s 2nd district, sees economic growth, and the threats posed by North Korea and Islamic State as the election-winning issues for Republicans. “Taxes will be one of the pillars of our campaign, but more indirectly. In the end, it’s going to be about an economy that’s growing.”

Republican Mike Coffman, whose reelection prospects are rated a toss-up in his Denver-area congressional district, has not been visible at all on taxes via social media. But his campaign spokesman, Tyler Sandberg, said Coffman talks about tax cuts regularly with supporters via email and with small business owners.

When they do talk about taxes, Republican candidates prefer to talk about the tax law in the context of how it is really a form of financial assistance to help families cope with college tuition, buy new cars, make mortgage payments, or even pay for summer camp.

Democrats, meanwhile, are attacking the new tax law as a boon for corporations and the wealthy that will add $1.5 trillion to the federal debt over the next decade.

They received some unexpected help from Republican Senator Marco Rubio last week. Rubio, who is not facing re-election this cycle, told the Economist magazine that benefits are going to corporations instead of employees.

“They bought back shares, a few gave out bonuses; there’s no evidence whatsoever that the money’s been massively poured back into the American worker,” he said.

Despite that criticism, some Republican incumbents are still making a determined effort to sell voters on the merits of the new tax law.

Dean Heller, 2018’s most vulnerable Republican senator, has been far and away the most aggressive on tax messaging. He has sent out 380 messages in the first four months of the year, or almost one-third of a total 1,287 messages.

But even his communications have dropped by 44 percent since the end of January.

“Let me be very clear, our campaign moving forward will be based on lower taxes and less regulation,” Heller said in an interview. “The trend you’ve seen in the first quarter of this year, I assure you, is not going to be the trend over the next six months.”