WASHINGTON – A marathon vote was underway Monday over US President Donald Trump's massive ‘one big, beautiful bill’, which highlights bitter partisan divisions in Washington.

Trump said the bill will deliver the largest tax cut for working- and middle-class Americans in history and will "unleash our economy".

The bill contains a slew of tax cuts for businesses and families and will "turbo-charge our economy and bring back the American dream," Trump said in a speech promoting the legislation.

However, Democrats are vehemently opposed to the mega-bill, which, if passed, will fund Trump's agenda and stand in stark contrast to what Democrats want for the country.

Democrats blast Trump's tax cuts as benefiting the wealthy, although Republicans maintain the cuts will help the middle class.

READ MORE: Trump's tax and spending bill faces Democratic resistance, GOP divisions

The bill has angered Democrats for what that party says are cuts to essential programs such as Medicaid -- health care coverage for low-income people – as well as food stamps.

Democrats and a couple of Republicans also fret the bill will add trillions of US dollars to the surging national debt.

Christopher Galdieri, a political science professor at Saint Anselm College in the northeastern state of New Hampshire, told Xinhua the legislation is "essentially a mega-bill combining most of Trump's legislative ambitions into one package – tax cuts, spending cuts, massively increasing the budget for ICE, and more."

The bill could provide additional funds for the US Immigration and Customs Enforcement (ICE) to boost the number of agents and to provide pay bonuses.

ICE is in large part carrying out Trump's mass deportation of millions of people who entered the United States illegally during the previous administration. But Democrats blast the deportations as heavy-handed, inhumane and unconstitutional.

Republicans argue that those funds for ICE are needed to reverse the damage they said Democrats did to the United States during the previous administration.

The GOP accuses Democrats of purposely opening the floodgates to millions of immigrants to illegally enter the United States, in what the GOP labeled an "invasion" and a result of Democrats' "radical left" agenda during the previous administration.

The White House also argues that among those who have illegally entered are many criminals and gang members.

Democratic Senate Minority Leader Chuck Schumer on Saturday criticized the bill, accusing Republicans of trying to dupe the American people and saying "most people hate this bill."

Some Republicans have also criticized the bill.

GOP Senator Josh Hawley has raised concerns about cuts to Medicaid, saying the reductions are "morally wrong and politically suicidal."

But on Saturday, Hawley changed his tune and announced he would back the bill.

Republican Senator Rand Paul blasted the bill for what he said was adding to the debt, labeling it "much more of a spending bill than a bill that rectifies the debt problem."

Paul has specifically lambasted the bill for what he said was adding to the national deficit by around $2.4 trillion over a decade.

ALSO READ: US Senate advances Trump's major tax-cut, spending bill

GOP Senator Thom Tillis criticized the bill on Saturday, saying: "It is inescapable this bill will betray the promise that Donald Trump made."

The senator denounced proposed cuts to Medicaid and lambasted the "amateurs" advising Trump, who he said have "no insight into how these... Tax cuts are going to be absorbed without harming people on Medicare."

Clay Ramsay, a researcher at the Center for International and Security Studies at the University of Maryland, told Xinhua: "The core of the partisan divisions is that Medicaid recipients, which are a quite significant portion of each legislator's constituents, are going to either suffer cutoffs or will have to spend a lot of time and energy to avoid that happening."

Republicans argue that the bill's tax cuts will stimulate the economy.

Dean Baker, a senior economist at the Center for Economic and Policy Research, told Xinhua: "There will be little net effect. The biggest effect is likely to be contractionary from the (tariffs)."

Musk threatens to unseat Congressmen who vote for Trump's "big, beautiful bill"

Billionaire Elon Musk renewed his criticism of the bill on Monday, threatening that the lawmakers who support it risk losing their primaries next year.

"Every member of Congress who campaigned on reducing government spending and then immediately voted for the biggest debt increase in history should hang their head in shame!" he wrote on his social platform X.

"And they will lose their primary next year if it is the last thing I do on this Earth," he noted.

In a separate post, Musk said he will support Republican Congressman Thomas Massie of Kentucky – whom Trump criticized for voting against the bill in the House and vowed to campaign against "really hard" in the GOP primary, promising "a wonderful American Patriot" would run against him.

READ MORE: US Republicans eye two-step Trump legislative agenda

Musk has been attacking the bill on and off since stepping down from the Department of Government Efficiency in May. He warned that the legislation will hike the debt ceiling by $5 trillion, "destroy millions of jobs in America and cause immense strategic harm to our country."

Musk broke his brief silence over the controversial spending bill on Saturday, calling it "utterly insane and destructive" as the package is working its way through the Senate.