WASHINGTON — Congress sped toward final approval Wednesday of a landmark $1.9 trillion COVID-19 relief bill, as President Joe Biden and Democrats neared a major triumph for the party's priorities and showcased the unity they'll need to forge future victories. 

The House was on track to use a virtual party-line vote to approve the 628-page measure, which represents Democrats' effort to bridle the catastrophic pandemic and revive the enfeebled economy. Four days after the Senate passed the measure over unanimous Republican opposition, GOP House counterparts were poised to do the same for a bill they've characterized as bloated, crammed with liberal policies and heedless of signs the dual crises are easing.

Democrats rejected those complaints.

"I call upon my Republican colleagues to stop their March madness and show some compassion for their constituents who are less than wealthy," said No. 3 House Democratic leader James Clyburn of South Carolina as the House debated the legislation.

For Biden and Democrats, the bill is essentially a canvas on which they've painted their core beliefs — that government programs can be a benefit, not a bane, to millions of people and that spending huge sums on such efforts can be a cure, not a curse. The measure so closely tracks Democrats' priorities that several rank it with the top achievements of their careers, and despite their slender congressional majorities there was never real suspense over its fate.

They were also empowered by three dynamics: their unfettered control of the White House and Congress, polls showing robust support for Biden's approach and a moment when most voters care little that the national debt is soaring toward a stratospheric $22 trillion. Neither party seems much troubled by surging red ink, either, except when the other is using it to finance its priorities, be they Democratic spending or GOP tax cuts. 

Republicans noted that they've overwhelmingly supported five previous relief bills Congress has approved since the pandemic struck a year ago — when divided government under then-President Donald Trump forced the parties to negotiate. They said this one, written solely by Democrats, was a bridge too far.

"This isn't a rescue bill, it isn't a relief bill. It's a laundry list of left-wing priorities that predate the pandemic," said House Minority Leader Kevin McCarthy of California.

A dominant feature of the bill is initiatives making it one of the biggest federal thrusts in years to assist lower- and middle-income families. Included are  expanded tax credits over the next year for children, child care and family leave plus spending for renters, feeding programs and people's utility bills.

The measure  provides up to $1,400 direct payments to most Americans, extended emergency unemployment benefits and hundreds of billions for COVID-19 vaccines and treatments, schools, state and local governments and ailing industries from airlines to concert halls. There is aid for farmers of color and pension systems, and subsidies for consumers buying health insurance  and states expanding Medicaid coverage for lower earners.

The Associated Press-NORC Center for Public Affairs Research poll found last week that 70% of Americans back Biden's response to the virus, including a hefty 44% of Republicans. 

Yet the bill's pathway has underscored Democrats' challenges as they seek to build a legislative record to persuade voters to keep them running Congress in next year's elections. 

Democrats control the Senate, split 50-50, only because Vice President Kamala Harris gives them the winning vote in tied roll calls. They have just a 10-vote advantage in the House.

That's almost no wiggle room for a party that ranges from West Virginia Sen. Joe Manchin on the conservative side to progressives like Vermont independent Sen. Bernie Sanders, Massachusetts Sen. Elizabeth Warren and New York Rep. Alexandria Ocasio-Cortez.

Progressives had to swallow big concessions in the bill to solidify moderate support. The most painful was dropping the House-approved federal minimum-wage increase to $15 hourly by 2025. 

Moderates forced tightened eligibility for the $1,400 stimulus checks, now phased out completely for individuals earning $80,000 and couples making $160,000. The House's initial extension of the soon-to-end $400 weekly emergency jobless payments, paid on top of state benefits, was trimmed by the Senate to $300 and will now halt in early September. 

Manchin was a leading holdout and in the middle of talks that resulted in curbing all of those initiatives. 

The independent Tax Policy Center said that the Senate-passed bill would give almost 70% of this year's tax breaks to households earning $91,000 or less. In contrast, the Trump-era GOP tax bill gave nearly half its 2018 reductions to the top 5% of households earning around $308,000, said the research center, which is run by the liberal-leaning Urban Institute and Brookings Institution. 

Yet keeping Democrats united won't get easier as the party tries advancing the rest of its agenda. There are fault lines within the party over priorities like immigration, health care and taxes. 

At some point it seems likely that progressives will draw their own lines in the sand. They are already demanding that the party revisit the minimum-wage boost, and amid all this Republicans are already demonstrating they are ready to pounce. 

The American Action Network, tied to House GOP leaders, said it's launched digital ads in mostly moderate districts calling the relief bill "a freight train of frivolous spending to bankroll their liberal cronies." 

The bill passed the Senate under budget rules that prevented Republicans from launching filibusters, which require 60 votes for most measures. That process won't be available for much legislation moving forward, but either way any Democratic Senate defections will make most bills there non-starters.