Photo taken on Aug. 10, 2021 shows the U.S. Capitol building in Washington, D.C., the United States. The U.S. Senate on Tuesday approved a long-awaited infrastructure bill, after months of strenuous negotiations between Democrats and Republicans. (Xinhua/Liu Jie)

The U.S. Senate on Tuesday approved a long-awaited infrastructure bill, after months of strenuous negotiations between Democrats and Republicans.

In a rare stroke of bipartisanship, more than a dozen Republicans joined Democrats to back the legislation. The final vote was 69-30, comfortably surpassing the 60-vote threshold required for most legislation in the 100-seat upper chamber.

Senate Majority Leader Chuck Schumer said on the Senate floor before the vote that this is a "decades overdue" step to revitalize the country's crumbling infrastructure, calling it the "most robust injection of funds" into infrastructure in decades.

According to the American Society of Civil Engineers, the country's infrastructure scores a C minus, with 43 percent of public roadways in poor or mediocre condition, and 7.5 percent of the nation's bridges "structurally deficient."

The group noted that the United States has been "underinvesting" in its infrastructure for decades. In 2019, the country spent just 2.5 percent of its GDP on infrastructure, down from 4.2 percent in the 1930s, said the organization, adding that the COVID-19 pandemic has made a difficult situation "worse."

In late March, U.S. President Joe Biden unveiled a roughly 2-trillion-U.S. dollar infrastructure plan, but it was criticized by Republicans, who argued it's not targeted on infrastructure and costs too much.

After months of negotiations, a bipartisan group of senators reached an agreement on a 1.2-trillion-dollar infrastructure bill, which includes 550 billion dollars in new spending on infrastructure projects, such as roads, bridges, passenger rails, drinking water and waste water systems. The rest of the package involves previously approved spending.

"While we are pleased Republicans and Democrats have come together to move forward important public investments, this legislation falls far short of its promise to be fully paid for," Maya MacGuineas, president of the Committee for a Responsible Federal Budget, a U.S. watchdog group, said in a statement Tuesday.

The group estimates that the bill will add about 400 billion dollars to deficits over the next decade.

MacGuineas urged the House of Representatives to improve the legislation, by supplementing the current pay-fors with additional revenue, spending reforms, and user fees, for the benefit of the nation's long-term fiscal and economic outlook.

Along with the infrastructure bill, Schumer and other Democratic leaders have been seeking to advance a separate 3.5-trillion-dollar spending plan using the budget reconciliation process, which only requires a simple majority to pass a legislation, and would allow Democrats to enact most of Biden's social-spending agenda without Republican support.

Immediately after the final vote on the bipartisan infrastructure bill, the Senate began to debate the 3.5-trillion-dollar budget plan, which focuses on childcare, education, health care and climate policy. The text of the plan was released by Democrats on Monday.

Schumer, the top Democrat in the Senate, said the infrastructure bill - despite its significance - doesn't address other challenges the country is facing, noting that Democrats believe "we need to do much more."

The Democratic budget will lower costs for Americans, cut taxes for American families, create millions of jobs while tackling the climate crisis, and "it's paid for by the wealthy and corporations paying their fair share," said Schumer.

Republicans, however, repeatedly lashed out at the massive spending plan, calling it the "socialist fantasy" for the far left, and warning that the tax hike would hurt U.S. businesses and families, and the high price tag would exacerbate inflation and push up the already ballooning debt.

"Senate Democrats are about to take their first step toward yet another reckless, partisan taxing and spending spree. It will push costs even higher for families. It will shatter President Biden's promise of no middle-class tax hikes," Senate Minority Leader Mitch McConnell said on Twitter.

With the Senate split 50-50, Democrats must keep moderates -- who could oppose elements of the agenda -- on their side, allowing Vice President Kamala Harris to cast the deciding vote.

In a letter to colleagues Monday, Schumer told Democrats that the goal is for congressional committees to write legislation by Sept. 15, before the House returns from its August recess.

House Speaker Nancy Pelosi, the top Democrat in the lower chamber, recently said that the bipartisan infrastructure plan won't get a vote until the Senate approves the larger, Democratic-only spending package, prompting criticism from Republicans.

White House Press Secretary Jen Psaki said at a briefing that the administration is confident and comfortable with the strategic approach of Speaker Pelosi, and the president "looks forward to signing each of these pieces of legislation into law."

When asked whether the massive spending plans would lead to unwanted inflation, Psaki told reporters that "we take inflation incredibly seriously."

"I would note that when we're talking about the budget reconciliation process, there are payfors put forward, including asking corporations and the highest, wealthiest individuals to pay a bit more -- something a broad swath, the vast majority of the American public supports," Psaki said.

According to recent estimation by the Committee for a Responsible Federal Budget, the two spending plans will, in reality, require nearly 1 trillion dollars of direct borrowing and set the stage for roughly 2.9 trillion dollars of total borrowing over the next decade.

This cost would lift debt to 115 percent of Gross Domestic Product (GDP) as opposed to 106 percent by 2031, the group noted.

"It's commendable that policymakers have called for fully offsetting new spending and tax breaks," the group said. "But rather than rely on gimmicks and sleights of hand to achieve this, they should either scale back the proposals, identify the necessary tax increases and spending reductions to cover the full costs of their proposals, or both."