Democrats were already facing a bleak landscape for this year’s midterm elections, with Joe Biden’s approval rating languishing in the low 40s and his party holding narrow majorities in both the House and the Senate.

Now, with Senator Joe Manchin’s refusal to support the Build Back Better Act, the chances of Republicans regaining control of the House of Representatives, and possibly the Senate as well, appear higher than ever.

If Democrats cannot pass Biden’s signature legislation, which includes massive investments in childcare, healthcare and climate initiatives, their failure may convince enough voters to support Republicans in November. However, if Democrats try to move forward with a version of the bill that Manchin supports, as some strategists have suggested, the final product may not be as attractive to voters.

Democrats’ unappealing options will probably aid Republicans, who were already favored to take back the House after the midterms. Historically, the president’s party loses House seats in midterm elections, and Republicans need to flip only five districts to regain the majority.

The decennial redistricting process has aided House Republicans’ cause, as the party controls the governorship and the state legislature in 23 states, compared with 14 states for Democrats. That advantage has allowed Republicans to draw more favorable congressional maps in a number of crucial swing states. Democrats have also accused Republicans of using voting restrictions, which were approved by at least 19 states last year, to limit their supporters’ access to the ballot box.

In the evenly divided Senate, Republicans need to gain just one seat to take control of the chamber. Rick Scott, who leads Senate Republicans’ campaign arm, has already said he expects the party to have “a hell of a year”.

Democrats’ possible failure to pass the Build Back Better Act may further assist Republican candidates, as it could strengthen their argument to voters that the $1.75tn spending package is the wrong solution for families struggling to recover financially from the coronavirus pandemic.

Emma Vaughn, a spokesperson for the Republican National Committee, attacked the Democratic bill as a “reckless spending spree”, telling the Guardian, “Americans reject their failed agenda and Republicans will continue to fight for American workers and businesses.”

But despite Manchin’s surprise announcement last month that he would not support the Build Back Better Act, the White House and Democratic congressional leaders are still voicing optimism about getting the bill passed.

“We have a very slim majority in the Senate. That means you need every single senator from across the spectrum of the Democratic party agreeing to what a package looks like moving forward,” the White House press secretary, Jen Psaki, said last week.

“We’re not naive about how challenging that is and how challenging it can be, but we feel good about the possibility of getting something done. What the final package looks like, I can’t outline that for you at this point in time.”

However, just hours earlier, Manchin had insisted that there were no conversations happening between him and the White House. “I’m really not going to talk about Build Back Better any more because I think I’ve been very clear on that. There [are] no negotiations going on at this time,” Manchin told reporters on Capitol Hill.

Manchin’s opposition to the bill has intensified concerns among Democratic leaders that many vulnerable members may lose re-election this year, as voters blame the party for failing to follow through on their campaign promises despite having full control of the White House and Congress.

“Voters have shown time and again that they want a robust economic environment creating good opportunities to build a better life for themselves and their family,” said Congressman Brad Schneider, chair of the political arm of the centrist New Democrat Coalition, the NewDem Action Fund. “At the end of the day, we have to show working families we’re responsive to their kitchen table concerns.”

Some Democratic strategists have argued the party’s best option now is to work with Manchin to craft a version of the Build Back Better Act that he can support and then move forward with that proposal.

“Mr Manchin said at various points that he could support a scaled-back bill that made long-term commitments to fewer priorities,” David Axelrod, a former adviser to Barack Obama, said in a recent New York Times column. “If, through a retooled Build Back Better Act, Mr Biden can achieve significant and durable progress on some major priorities that will benefit children and families for generations, Democrats would be wise to celebrate and tout those gains instead of complaining about what wasn’t possible.”

Schneider echoed that argument, telling the Guardian, “Since the start of negotiations, New Dems have been advocating to do a select number of things better for longer, and we still believe that approach is the best path forward.”

But a Manchin-approved version of the Build Back Better Act does not come without potential pitfalls. Manchin has raised concerns about the cost of the legislation and the impact on the national debt if all of its programs are made permanent. (Under the current version of the bill, many of its programs expire after a year or a few years.)

The child tax credit, which was expanded under the coronavirus relief package signed by Biden last year, is particularly worrisome for deficit hawks. The current version of the Build Back Better bill calls for the expanded program to continue through 2022, at a cost of $185bn. However, if the expanded program is made permanent, as many Democrats would prefer, the 10-year cost of that policy would be $1.6tn, according to the Congressional Budget Office.

Despite the cost of the policy, many Americans have come to rely on the monthly checks from the expanded child tax credit, and failing to extend the program could be disastrous for families’ budgets and Democrats’ electoral prospects.

“If [Manchin] brings down the price tag below $1.75tn, if he cuts really popular things like the child tax credit especially or any of the pharma provisions, then that could be disastrous for Democrats,” said Adam Green, the co-founder of the Progressive Change Campaign Committee.

But Green argued there may be an upside to Manchin’s deficit concerns. If Manchin is determined to lower the national debt, it could provide an opening for progressives to advocate for revenue-raising proposals that they support, such as a tax on billionaires.

“There’s actually a scenario where we raise $1.75tn and invest that money, and then on top of that implement a very popular billionaires tax, the majority of which goes toward debt reduction,” Green said. “What that would do is give Democrats this extremely popular talking point that we’re the ones who finally taxed billionaires.”

Of course, that scenario will only be possible if Democrats are successful at bringing Manchin back to the negotiating table and actually getting a bill across the finish line. “Depending on how the negotiations go, Manchin’s current involvement could make things disastrous or very good for Democrats,” Green said. “It really depends on where things land.”