Congressional leaders on Wednesday unveiled a sweeping budget deal that would add about $400 billion in federal spending over the next two years, delivering the military funding boost demanded by President Trump alongside the increase in domestic programs sought by Democrats.

With a midnight-Thursday government shutdown looming, the accord holds the promise to break a months-long partisan standoff centered around federal spending, though some roadblocks remain.

In a major lift for the package, the White House signaled its support, with press secretary Sarah Huckabee Sanders calling it “steps forward.” But several Republicans strenuously opposed a plan that would add to the nation’s debt.

“This spending bill is a debt junkie’s dream,” said Rep. Mo Brooks (R-Ala.), warning of trillion-dollar-a-year deficits. “I’m not only a no, I’m a hell no.”

According to outlines of the budget deal shared by congressional aides, existing spending limits written into law would be raised by a combined $315 billion through 2019. About $90 billion more would be spent on disaster aid for victims of recent hurricanes and wildfires.

Lawmakers described a deal that would keep the country from hitting the debt limit until after November’s midterm elections, typically a politically difficult vote for Republicans.

Top Senate leaders from both parties called the deal a breakthrough and a prelude to more cooperation between Republicans and Democrats.

“This bill represents a significant bipartisan step forward,” said Senate Majority Leader Mitch McConnell (R-Ky.). “I hope we can build on this bipartisan momentum and make 2018 a year of significant achievement for Congress, for our constituents and for the country we all love.”

Senate Minority Leader Charles E. Schumer (D-N.Y.) said, “This budget deal is the first real sprout of bipartisanship, and it should break the long cycle of spending crises that have snarled this Congress and hampered our middle class.”

Initial votes on the plan in the Senate could come as soon as Wednesday afternoon, but opposition to the deal was mounting in the House, where conservative Republicans and liberal Democrats found reasons to fume.

In one late-developing wrinkle, House Minority Leader Nancy Pelosi (D-Calif.) said Wednesday that she and “a large number” of fellow Democrats will oppose a spending deal to keep the government open unless she is guaranteed a vote on immigration legislation.

The move came amid rising fury from House liberals and immigration activists as congressional leaders appeared on the cusp of announcing a massive two-year budget deal without a fix for “dreamers.”

Although it was not immediately clear how many Democrats would follow Pelosi’s lead, her announcement raised new uncertainty about whether congressional leaders would have the votes for passage.

House Republican leaders briefed rank-and-file members on the specifics of the deal, and divisions were evident within the GOP. Defense hawks hailed the pact for bringing stability to military spending after multiple short-term patches.

“We have spent a decade or more breaking our military and it’s going to cost some money to put it back together,” said Rep. Steve Russell (R-Okla.)

But Sen. Bob Corker (R-Tenn.) questioned the additional billions for the Pentagon.

“The amount of military spending, defense spending, is far above the president’s request. Far above it,” Corker said. “I’m all for supporting our military and I want to make sure they’re funded properly. It’s very difficult to have that big of increase in one year and then be able to use it wisely.”

[Senate leaders see two-year budget deal within their grasp]

In the Senate, McConnell brought a government shutdown to an end last month by guaranteeing a floor debate on immigration. Pelosi said she wanted the same commitment from House Speaker Paul D. Ryan (R-Wis.).

“Without that commitment from Speaker Ryan, comparable to the commitment from Leader McConnell, this package does not have my support, nor does it have the support of a large number of members of our caucus,” Pelosi said.

Young immigrants who were brought into the country illegally as children, known as dreamers, are on the verge of losing their work permits after Trump announced he would end the program that protects them from deportation. Democrats had sought to use their leverage on spending legislation to achieve a fix for the dreamers, but without success.

Ryan spokeswoman AshLee Strong said that the speaker “has already repeatedly stated we intend to do a DACA and immigration reform bill — one that the president supports.” Trump moved last year to end the Deferred Action for Childhood Arrivals program, or DACA, which has given legal status to hundreds of thousands of dreamers. The program could end soon as next month.

Senate Democratic aides say that the budget deal contains numerous wins for the minority party, starting with major increases to domestic programs that the party has championed. The figures negotiated represent an equal increase for defense and nondefense spending over the levels set in the 2011 Budget Control Act.

But with the budget deal not expected to address the dreamers or any other immigration issue, Pelosi has to answer to angry members of her base.

She is facing internal pressure from immigrant supporters in her caucus who have pushed relentlessly in recent months to use what little leverage they have in the House minority to secure protections for dreamers. Of 193 voting House Democrats, only 45 supported the deal that reopened the government after a three-day shutdown last month.

[Yes, another government shutdown is entirely possible]

Rep. Luis V. Gutiérrez (D-Ill.), an outspoken leader of the party’s Latino bloc, said Tuesday that any budget deal that does not protect dreamers would represent “a complete betrayal of a key, core principle” for Democrats. He compared it to party leaders agreeing to close down Planned Parenthood clinics or ending federal recognition of same-sex marriages.

“Look, I can’t make it any clearer,” he said. “I would have to go back to the Democratic caucus and denounce any such proposal and anybody that was involved in making it. I cannot be a Democrat in good standing if they’re not going to share values.”

Pelosi made the announcement as she commandeered the House floor in an unusual maneuver, using rules that allow House leaders to speak on the floor as long as they want. She used the time to tell the stories of one dreamer after another.

“Why should we in the House be treated in such a humiliating way when the Republican Senate leader has given that opportunity in a bipartisan way to his membership?” Pelosi said. “What’s wrong? There’s something wrong with this picture.”

She said House Democrats met earlier Wednesday to discuss the situation and decided on the approach.

Pelosi’s dramatic House floor speech stretched on for several hours.

President Trump on Tuesday also threw immigration into the budget debate, saying he would welcome a shutdown if Congress did not address immigration reform, including funding for a border wall.

“I’d love to see a shutdown if we don’t get this stuff taken care of,” Trump said at a White House event focused on crime threats posed by some immigrants. “If we have to shut it down because the Democrats don’t want safety . . . let’s shut it down.”