WASHINGTON (AP) — In one of the last acts of the Democratic-led Congress, the House and the Senate are set to pass an overhaul of the Electoral Count Act, the arcane election law that then-President Donald Trump tried to subvert after his 2020 election defeat.

The legislation, which Democrats and Republicans have been working on since the Jan. 6, 2021, insurrection at the Capitol, is the most significant policy response so far to the attack and Trump's aggressive efforts to upend the popular vote.

Led by Republican Sen. Susan Collins of Maine and Democratic Sen. Joe Manchin of West Virginia, along with members of the House Jan. 6 panel, the bipartisan legislation was added to a massive year-end spending bill that was unveiled early Tuesday and will be voted on this week.

The bill would amend the 19th century law that governs, along with the U.S. Constitution, how states and Congress certify electors and declare presidential election winners, ensuring that the popular vote from each state is protected from manipulation and that Congress does not arbitrarily decide presidential elections when it meets to count the votes every four years.

Supporters in both chambers — Democrats and some Republicans — have pushed to pass an overhaul before the start of the next Congress and ahead of the 2024 presidential campaign cycle, as Trump has announced that he is running again. More than a dozen GOP senators have publicly backed the legislation, including Senate Republican Leader Mitch McConnell of Kentucky.

"We are now one step closer to protecting our democracy and preventing another January 6th," said Senate Rules Committee Chairwoman Amy Klobuchar, D-Minn., who moved the bill through her committee.

A look at what the bill would do:

CLARIFY THE VICE PRESIDENT'S ROLE

Lawmakers and legal experts have long said the 1887 law is vague and vulnerable to abuse, and Democrats saw Trump's efforts to overturn his defeat ahead of Jan. 6, 2021, as a final straw.

Supporters of the Republican former president attacked the Capitol that day, echoing his false claims of widespread election fraud, interrupting the congressional certification of Democrat Joe Biden's victory and calling for Vice President Mike Pence's death because he wouldn't try to block Biden from becoming president.

The bill clarifies that the vice president has a purely ceremonial role presiding over the certification every Jan. 6 after a presidential election and that he or she has no power to determine the results of the election — an effort to make that point emphatically in the law after Trump and some of his allies put massive pressure on Pence. Pence resisted those entreaties, but many lawmakers were concerned that the law wasn't definitive enough.

The legislation states that the vice president "shall have no power to solely determine, accept, reject, or otherwise adjudicate or resolve disputes" over the counting of electors in Congress.

MORE DIFFICULT TO OBJECT

The legislation would also make it more difficult for lawmakers to object to a particular state's electoral votes. Under current law, just one member of the Senate and one member of the House need to lodge an objection to automatically trigger votes in both chambers on whether to overturn or discard a state's presidential election results. The bill would significantly raise that threshold, requiring a fifth of each chamber to object before votes would be held.

Raising the threshold for objections will do away with a partisan tradition that has rankled members on both sides. Democrats have objected the last three times that Republicans were elected — twice against George W. Bush and once against Trump. But in each of those cases the Democratic candidate had already conceded the election loss, and Trump to this day falsely claims he defeated Biden.

In 2021, Republicans objected to Biden's electoral votes in Arizona and Pennsylvania, triggering votes in both chambers after the Capitol was cleared. The House and the Senate voted overwhelmingly to certify Biden's win in those states, but members in both parties worried the process was too vulnerable to manipulation.

The House-passed version of the bill, written by Democrats and Republicans on the Jan. 6 panel, would have raised the threshold for a successful objection to a third of each chamber. But the final legislation is much closer to the Senate version overall, an effort to ensure that GOP senators backing the bill would stay supportive.

NO FAKE ELECTORS

The bill would ensure that there is only one slate of electors, a response to Trump allies' unsuccessful efforts to create alternate, illegitimate slates of Trump electors in states that Biden narrowly won in 2020.

Each state's governor would be required to submit the electors, which are sent under a formal process to Congress and opened at the rostrum during the joint session. Congress could not accept a slate submitted by a different official, so there could not be competing lists of electors from one state.

The bill would establish legal processes if any of those electors are challenged by a presidential candidate.

'CATASTROPHIC' EVENTS

The legislation would revise language in current law that wasn't used during the 2020 election but that lawmakers think could be abused. Current law allows state legislatures to override the popular vote in their states by calling a "failed election," but the term is not defined under the law.

The bill says a state could only move its presidential election day if there are "extraordinary and catastrophic" events, such as natural disasters, that necessitate that.

House lawmakers and legal experts have argued that language is too vague and have proposed that a judge should also have to sign off on any such delay. But the final version of the bill does not require that.