With Republican Party majorities in the House of Representatives and the Senate, it would be simple for an onlooker to assume US President Donald Trump would not have any trouble getting laws passed.
But as his closest allies struggle to muscle the One Big Beautiful Bill Act through Congress, this idea has been disproved.
After an entire day of negotiations and a vote with the narrowest of margins, the president's marquee bill has now returned to the House for more debate.
Here's the latest on the divisive bill and why some Republicans are voting against it.
What just happened?
US President Donald Trump is getting closer to seeing his One Big Beautiful Bill Act passed after Vice-President JD Vance cast a tie-breaking vote to pass the bill in the Senate on Tuesday.
After a drudge of debate and negotiations that extended over more than 24 hours, three Republicans — Thom Tillis of North Carolina, Susan Collins of Maine and Rand Paul of Kentucky — had joined all 47 Democrats in voting against the bill, creating a deadlock of 50-50.
Much of the late horsetrading was aimed at winning over Republican senator Lisa Murkowski of Alaska, who had signalled she would vote against the bill without significant alterations.
What is the Big Beautiful Bill?
Its full name is the One Big Beautiful Bill Act, but it's also shortened to the OBBBA or BBB.
In essence, it is a budget reconciliation bill — a tool to fast-track policy around spending, revenue and the debt ceiling.
The 1,038-page bill rolls together hundreds of proposed changes, from tax cuts to changes to social benefits programs.
What's in it?
Here's an overview of some of the key changes put forward in the One Big Beautiful Bill Act.
Court restrictions
Experts have warned a single sentence in the bill would weaken the powers of federal judges to enforce contempt when the government defies the court.
"No court of the United States may enforce a contempt citation for failure to comply with an injunction or temporary restraining order if no security was given when the injunction or order was issued," the provision says.
According to Reuters, "security" in this case refers to monetary bonds that can be used when injunctions are issued.
If the injunction is later reversed, the bond helps cover the defendant's losses.
The Trump administration argues the provision would deter frivolous lawsuits, but Democrats argue it would leave judges powerless to rein in defiance.
Golden dome
On social media, Mr Trump has claimed the bill would secure funding to develop a network of missile defence systems.
The BBB would provide a $US25 billion ($38 billion) initial investment to develop the "golden dome".
The Congressional Budget Office has estimated the cost of developing a sophisticated missile defence system could exceed $US500 billion.
The bill would also commit $US21 billion to restock the US ammunition arsenal and $US34 billion to expand its naval fleet.
Immigration
Mr Trump would revive construction of the wall along the US-Mexico border, which he began during his first term, with a $US46.5 billion ($70.7 billion) injection.
A further $US45 billion would be allocated to fund 100,000 immigration detention facility beds to support the Trump administration's pursuit to conduct the largest mass deportation in US history.
The bill would also set aside $US4 billion to hire thousands more Border Patrol and customs officers, and a further $US2.1 billion for signing and retention bonuses.
To help pay for it, immigrants would face various new fees.
Asylum seekers would be required to pay at least $US1,000 on filing an application for asylum.
While it would be a first for the US, other nations charge a fee for asylum applications, but the costs are significantly lower — $45 in Australia's case.
The debt ceiling
The debt ceiling is a limit on the amount of money the federal government can borrow.
The BBB would raise it by $US4 trillion ($6 trillion) to $US40 trillion.
Medicaid
The bill would introduce additional restrictions on Medicaid, a joint federal and state program that helps cover medical costs for millions of elderly, disabled and low-income Americans.
That would include a requirement for able-bodied adults with no dependents to work at least 80 hours a month to qualify for benefits, starting December 2026.
Republicans argue they are trying to right-size the safety net programs for the population they were initially designed to serve, mainly pregnant women, the disabled and children, and root out what they describe as waste, fraud and abuse.
Recipients would also need to reapply for benefits every six months, rather than every year.
There's also a proposed new $US35 ($53) co-payment that can be charged to patients using Medicaid services.
The Congressional Budget Office estimates 11.8 million more Americans would become uninsured by 2034 if the bill becomes law.
Republicans also hope to strip Planned Parenthood of funding from Medicaid.
As well as providing abortion care, the organisation offers cancer screenings, pap smears and birth control.
No tax on tips, overtime
One of Mr Trump's key campaign promises — to end taxes on tips and overtime pay — would be ticked off by the BBB.
The bill would also temporarily increase the Social Security income tax deduction of up to $US4,000 ($6,000) for recipients aged 65 and over.
SNAP benefits
The One Big Beautiful Bill Act would introduce work requirements to able-bodied recipients of the Supplemental Nutrition Assistance Program (SNAP) who do not have dependents.
More than 40 million low-income earners rely on SNAP to boost their grocery budgets and access nutritious food options.
The Congressional Budget Office estimates 3 million Americans would no longer qualify for food stamps if the bill is passed.
The bill would also require states to contribute more to the program, which is partly funded by the federal government.
Student loans
All existing student loan repayment plans would be replaced with just two classifications: a fixed-rate monthly repayment plan over the course of 10 to 25 years, or an income-based "repayment assistance" program.
It would scrap current rules that allow borrowers to temporarily defer their loan repayments due to financial hardship or unemployment.
Tax cuts
Republicans say the bill is crucial because without it, there will be a massive tax increase after December when tax breaks from Trump's first term expire.
The legislation contains about $US4.5 trillion ($6.8 trillion) in tax cuts.
The wealthiest households would see a $US12,000 increase from the legislation, which would cost the poorest people $US1,600 a year, according to the nonpartisan Congressional Budget Office analysis of the House's version.
Middle-income taxpayers would see a tax break of $500 to $1,500, the CBO said.
What did the Senate change?
One key change out of the Senate was to scrap a provision that would have blocked states from regulating artificial intelligence industries for a decade.
House of Representatives member Marjorie Taylor Greene, who initially voted in favour of the bill, later expressed her regret after learning of its inclusion and called on senators to strip it.
The Senate voted to do so with a resounding 99-1 vote.
To secure Senator Murkowski's vote, a provision was thrown in at the final hours to provide $10 billion annually to rural hospitals for five years.
Another provision added to court Ms Murkowski's support would send more food aid funding to Alaska and several other states.
The amended bill also stripped out a new tax on wind and solar projects that use a certain percentage of components from China.
Why are Republicans divided?
Republicans who are critical of the bill each have their own reasons.
Some, including Senator Paul, say the bill's provision to raise the debt ceiling is fiscally irresponsible, because US debt is already out of control.
Independent analyses have found the BBB will add between $US2.5 trillion ($3.8 trillion) and $US3.1 trillion in debt to the US budget, but the Congressional Budget Office projects that number would be closer to $US3.5 trillion over the next 10 years.
Government debt is already roughly 121 per cent of the nation's GDP and has grown exponentially in recent years to exceed $US35 trillion.
[INTERACTIVE: US national debt graph]Billionaire Elon Musk has also taken issue with the BBB for this reason, which led to his high-profile falling out with Mr Trump in June.
Meanwhile, senators Tillis and Collins say they don't support the bill because it would cut funding for Medicaid.
"What do I tell 663,000 people in two years, or three years, when President Trump breaks his promise by pushing them off of Medicaid because the funding's not there anymore, guys?" Mr Tillis said during an impassioned speech on Sunday.
"I think the people in the White House … advising the president are not telling him that the effect of this bill is to break a promise."
What happens next?
Because the Senate voted on an amended measure, the bill will now be volleyed back to the House of Representatives for another vote.
House Speaker Mike Johnson has pledged to see the bill passed quickly, but that relies on the vast majority of Republicans who initially voted in favour not withdrawing their support because of the Senate's changes.
The House of Representatives is currently made up of 220 Republicans and 212 Democrats.
But GOP House members including Chip Roy of Texas, Ralph Norman of South Carolina and David Valado of California have already indicated they won't support the Senate's amendments.
The bill first passed the House in May by a vote of 215-214.
There's also the possibility more changes could be added as Republicans continue their negotiations to get the bill passed.
ABC/AP
