Sen. Michael F. Bennet (D-Colo.) tapped out the longest text messages he’d ever written one night in January, urging Susan Rice, a top Biden aide and a friend, to include a full-scale anti-child-poverty measure in the coronavirus rescue plan to be unveiled within days.

Rep. Rosa L. DeLauro (D-Conn.) was making the same case to a different senior Biden official, using language that the official later described as “somewhat juicy.”

And Sen. Cory Booker (D-N.J.) tried flattery, urging Biden staffers to adopt what he told them would be a “legacy” program earning them a place in history.

An unlikely coalition of Democrats across the ideological spectrum mounted an 11th-hour push in the final weekend before the American Rescue Plan for President Biden to go big on tackling child poverty. They prevailed over what one person involved in the process called the “cost police” in Biden’s inner circle, those anxiously warning about the ballooning cost of the stimulus package.

As part of the next covid relief bill, President Biden proposed an expanded child tax credit that would send direct payments to help struggling families. (Joy Yi/The Washington Post)

This under-the-radar success created what could be the most consequential piece of the $1.9 trillion package — one that, if made permanent, could approach the impact of the programs established under President Lyndon B. Johnson’s War on Poverty.

The sudden, unexpected creation of an approximately $120 billion social program has thrown a twist into the political landscape. Some Democrats now fear being labeled big-government spenders in the upcoming midterms. Some conservatives, on the other hand, are embracing the idea as a family-friendly measure.

With the initiative expiring in a year, all but ensuring it will be a major issue in the midterms, the child poverty measure raises a central question: Are the politics of big government back?

The program’s impact probably will be profound. It expands the federal child-rearing subsidy by 50 percent — and parents of toddlers will get even more. A family with two young children and no income will now get $600 a month. The parents of 90 percent of the country’s children will benefit, and millions of children will be lifted from poverty, according to analysts.

Crucially, the new money takes the form of cash payments, not tax cuts, so even people who don’t make enough to pay taxes will get aid.

That approach aligns the United States far more closely with European-style wealth redistribution, according to both supporters and detractors. “I liken it to the New Deal,” DeLauro said in an interview. “This changes the country.”

Biden’s challenge now is to make the concept permanent; Democrats declined to do so this year to avoid making the relief bill even costlier.

The anti-poverty measure first attracted the attention of the president’s team during the transition, as staffers were weighing what should be in a stimulus. They saw child aid as a response to the pandemic — but also a way to enact a long-term Democratic goal.

“The thought was that this vehicle would be an early and important one where we could, in the context of covid crisis, do something extremely beneficial for those who’ve been hit the hardest by the crisis,” Rice said in an interview.

Cecilia Muñoz, a senior transition aide, said that although the idea was not new, the moment was. “For folks who focus on children and focus on poverty, this stuff is extremely well-known,” Muñoz said. “What really happened was that the scale of the crisis was such that people took a fresh look at this and said, ‘Wow, this is really something we could do now.’ ”

But it was hardly obvious that the program fit in the coronavirus relief package. Bennet, DeLauro and Booker, along with Sen. Sherrod Brown (D-Ohio), all of whom have known Biden for years, started calling around the president’s circle to make their case.

But on the Friday before Biden was set to unveil the American Rescue Plan, a White House aide texted Bennet, her former boss, to say that only a scaled-down version of the child poverty plan had made it into the package.

That set off alarms. “We won the election, we won the Senate and the presidency, so now it was time to move,” DeLauro recalled. “I made calls on Saturday and Sunday” to White House aides such as Jared Bernstein, a top Biden economic adviser. (Bernstein later told The 19th, a news website, that she made her case “in language that I might describe as ‘somewhat juicy.’ ”)

And Bennet sent his urgent text to Rice, noting that Vice President Harris had supported the idea when she was a senator and providing figures on how it could cut child poverty over the long term.

By the end of the weekend, the full proposal was in the bill.

Republicans so far have not made the measure a focus of attack, instead casting the broader coronavirus relief package as a boondoggle that includes billions in spending unrelated to the pandemic.

“Democrats decided their top priority wasn’t pandemic relief — it was their Washington wish list. It was jamming through unrelated policy changes they couldn’t pass honestly,” Senate Minority Leader Mitch McConnell (R-Ky.) said in a floor speech.

That is an argument Republicans probably will make frequently as the midterms approach, especially if the relief package loses popularity or faces logistical problems. Muñoz acknowledged that the distribution of millions of checks under the child poverty program could be hard to implement.

“I think the administration has taken it up with its eyes wide open,” she said.

During Treasury Secretary Janet Yellen’s confirmation hearings, Brown asked whether she would push the IRS to implement the checks in a timely way. Yellen responded, “Yes, I will,” although the IRS in recent days has signaled that getting the checks out the door by the July target date could present difficulties.

Democrats already are pushing to include an extension of the program in the president’s next budget package, according to a Congressional aide involved in the discussions.

Beyond that, Democrats hope American families will get used to receiving their checks, and they cite the Washington axiom that it’s hard to take something away from voters after they’ve started receiving it.

Still, popularizing the program will require Biden to begin selling it. The president has mentioned it in his speeches but has not made it a focus.

White House aides say a harder sales pitch is coming. “Halving child poverty” is one of 10 elements of the American Rescue Plan that Biden plans to highlight in coming days, according to a memo obtained by The Washington Post.

Some Democrats acknowledge that some in their party are squeamish about having to defend the distribution of government checks to working-age adults who are not working, even if it’s to help care for their children.

The party remains bruised from the political fights of the 1980s and 1990s, when federal welfare recipients were caricatured in often biting terms. “Maybe it’s the specter of the ‘welfare queen,’ ” said one person who has pushed the issue for years and spoke on the condition of anonymity to speak frankly about how the change is messaged. “The poverty of our children is because of the implicit racism that often inhibits us from doing things.”

So far those fears have not been realized. The Biden administration is even eyeing potential support from the political right, where conservatives have pitched ideas similar to the Biden child tax credit, with the goal of supporting families and making it easier for one parent to stay home.

“We’ve seen the birthrate in this country go down, down, down, and people are not getting married and not having kids,” Sen. Mitt Romney (R-Utah) said Thursday, as he pitched his own plan at an event hosted by American Compass, a conservative think tank. His proposal, he said, is “designed to be a very substantial incentive for marriage, family formation, as well as for having kids.”

Romney’s plan is more generous than Biden’s for parents of the youngest children, and he even argued it could reduce abortions. “This is to help the pregnant women who are concerned about the financial circumstances of bringing a child into the world,” Romney said. “Providing a monthly stipend to someone who is pregnant is very much a pro-life consideration.”

Republican Sens. Mike Lee of Utah and Marco Rubio of Florida, both staunch conservatives, have backed a different version of child assistance that offers more money to working parents but would omit checks for the unemployed.

That is a stark difference from Biden’s plan. The president’s version boosts the existing $2,000 annual child subsidy — known as the Child Tax Credit — by $1,000 per child, or $1,600 for the parents of very young children.

In the past, parents who did not work, and therefore paid no federal income tax, did not benefit from the program, since it was set up as a reduction in taxes owed. But now they will have access to the federal checks.

A related change triples the size of the Earned Income Tax Credit, which also is intended to benefit the poor, expanding eligibility to a lower age limit of 19 and removing an upper age limit.

DeLauro has been pushing the child payments for 18 years and wrote about it in her 2011 book “The Least Among Us.” “It took a while to do,” DeLauro acknowledged in the interview, adding that over the years, “time changes, people change, the environment changes, and you can get things done.”

The bill’s backers were spurred to action in part because the coronavirus crisis highlighted the inequality in American society. “There’s a sense that the economy for 50 years has worked for people at the very top, but literally for 90 percent of Americans it hasn’t worked,” Bennet said. “That was much more clear to members of Congress today than it was when Barack Obama was president.”

The closest approximation to an early lobbying effort for the idea came from one of the country’s wealthiest families — William and David Harris, a secretive father-and-son duo who have quietly pushed the change “from the beginning,” DeLauro said.

“I talked to them all the time on this,” Brown added. “They’re good strategists.”

David Harris declined to comment for this article. But over the years he and his father shopped the idea to moderate senators, avoiding liberals whose rhetoric might alienate potential allies, one longtime observer said.

Bennet seized on the idea several years ago, saying he had seen the impact of child poverty up close when he headed the Denver school system. He decided to make the child tax credit a central message of his 2020 presidential campaign.

It didn’t go well. “Almost no attention was paid to this,” Bennet said. “But I accept that as a failing of mine as a candidate.” He dropped out of the race in February 2020 after a poor finish in New Hampshire.

Booker also tried to make an issue of child poverty during the Democratic primary, incorporating the proposal into his anti-poverty agenda, but said he struggled to talk about it in a compelling way. The idea, after all, is technically called “an expansion of the child tax credit that makes it fully refundable,” a puree of jargon that few understand.

“These words that we’re using are so wonkish; they’re not good a conveying the scale and the grandeur of what’s happening here,” Booker said in an interview. “My team was really determined to try to influence the policy of whoever would win to really be an administration that took on child poverty.”

As for Biden, DeLauro pitched him on the idea before he formally entered the presidential race in April 2019, recalled former senator Chris Dodd of Connecticut, who is close to both Biden and DeLauro.

Once Biden sewed up the nomination, supporters redoubled their efforts to lobby him and his top advisers, arguing that this was the perfect time to push the measure through, and the relief bill was the perfect vehicle.

“It was a crescendo. It was a drumbeat. It was the repetitiveness of talking about this issue so much,” Brown said. He said he started “working” Ted Kaufman, a top Biden adviser.

DeLauro, for her part, pressed Dodd into service to lobby the Biden team. Dodd called Jake Sullivan, a top domestic policy aide during the campaign who is now Biden’s national security adviser, and offered him a ream of information, even joking about providing a speech Biden could give on the issue.

Still, the child poverty plan did not make it into the initial “Build Back Better” agenda that Biden heralded over the summer. But in early September, when Biden called House Ways and Means Chairman Richard E. Neal (D-Mass.) to congratulate him on winning his primary, Neal used the call to urge Biden to champion the policy.

Shortly after, the Biden’s campaign added a few lines to its website embracing the idea. The change garnered little attention, going online the day after liberal Supreme Court Justice Ruth Bader Ginsburg died.

Still, it was a victory, backers said. And six months later, Biden has signed a covid relief package that includes the measure.

The president called DeLauro to thank her personally for pushing it so hard and credited her publicly at a Rose Garden ceremony following the bill’s passage.

After the legislation passed, a reporter asked Brown how he felt. He replied, “It was the best day of my career.”

Alice Crites contributed to this report.