President Trump said this week that he hopes Vice President Pence “comes through for us” when he presides over Wednesday’s joint session of Congress to certify the election Trump falsely claims was rigged and stolen.

He has declared that, as president of the Senate, Pence “has the power to reject fraudulently chosen electors” who recognized Joe Biden’s decisive 306-to-232 electoral college victory. But even as Trump and his boosters in Congress see Wednesday’s exercise as an opportunity to overturn the election’s outcome, the vice president is constrained by the Constitution, federal law and history, and cannot declare Trump the winner.

“If the rules that have been in place and understood since 1887 are fairly applied and tradition followed, there is no possibility of any vote being discounted and certainly not enough to change the election,” said Stephen Siegel, a legal historian who has spent years studying the electoral vote count.

In writing the rules for tallying the votes, Congress intentionally minimized the vice president’s power because of conflict-of-interest concerns. Pence cannot just call the shots or “do what Trump seems to be asking,” said Edward B. Foley, who leads Ohio State University’s election law program.

With Democrats in control of the House and Senate Majority Leader Mitch McConnell (R-Ky.) acknowledging Biden’s victory and discouraging debate over the electoral count, there are not enough votes in either chamber to change the outcome.

But that won’t stop the unprecedented attempt, which follows Trump’s repeated failure in the courts to prove his baseless claims of widespread voter fraud. With his encouragement, a significant swath of Republicans in the House and Senate plan to vote against certifying electors from key states.

Sen. Ted Cruz (R-Tex.), who has led a coalition of 10 other senators and pushed for an audit of the results, plans to object to certification of electors from Arizona, according to a person familiar with the plans. Sen. Josh Hawley of Missouri has vowed to contest results in Pennsylvania. And Sen. Kelly Loeffler, on the ballot in Georgia’s runoff, plans to object to the outcome from her state.

Wednesday’s gambit could stretch on for hours, upending what has been a largely ceremonial process that has in recent decades lasted all of 24 minutes, according to a report from the Congressional Research Service.

Members of Congress have previously tried to raise objections, but never on such a large scale. Procedurally, objections must be submitted in writing and signed by one senator and one member of the House. The two chambers then debate separately for up to two hours before voting on the objection and reporting back to the joint session. That process would be repeated for successive objections to other states’ counts.

After the contested 2000 election, then-Vice President Al Gore presided over the declaration of his own defeat. He turned away objections to electoral votes submitted by Florida because they were signed only by a member of the House without support from a senator.

In 2005, several Democrats tried unsuccessfully to challenge Ohio’s electoral votes for George W. Bush.

None of the objections being contemplated this year are “appropriate under the letter or spirit of the statute,” said Foley, an election law expert. “Congress doesn’t go and second- guess a state when there’s a single, official submission from a state.”

Some conservative Republicans have echoed that view in breaking with Trump and emphasizing that Congress has no authority to reject state-certified votes.

“There are only two things I am permitted to do under the Constitution: ensure the electors are properly certified and count the electoral votes, even when I disagree with the outcome,” Sen. James M. Inhofe (R-Okla.) said in a statement Tuesday. “To challenge a state’s certification, given how specific the Constitution is, would be a violation of my oath of office.”

Pence’s constitutional duty is outlined in the 12th Amendment, which says the vice president “shall, in the presence of the Senate and House of Representatives, open all the certificates and the votes shall then be counted.”

In practice, that means Pence will open sealed envelopes of certified electoral votes from the 50 states and the District before handing the documents to lawmakers named as “tellers” who then tally the vote.

The Constitution makes the vice president “the custodian of the ballot” and after that, his role is mainly ministerial, Siegel explained.

A long-shot lawsuit from Rep. Louie Gohmert (R-Tex.), one of the president’s most vocal allies in the House, tried to give Pence more power in the process. But last week a judge nominated by Trump quickly dismissed the case that argued Pence has the authority to invalidate Biden electors in certain states.

The Justice Department, representing Pence, urged the court to toss the lawsuit. Pence seemed to acknowledge his limited role in a statement over the weekend even as he voiced concerns about unproved voter fraud and seemed to encourage the attempt to nullify millions of Americans’ votes.

“The vice president welcomes the efforts of members of the House and Senate to use the authority they have under the law to raise objections and bring forward evidence before the Congress and the American people on January 6th,” said Pence’s Chief of Staff Marc Short.

The timing of the joint session, beginning at 1 p.m., and the rules for any debate are all spelled out in statute. One of the goals of the Electoral College Act of 1887 was to prevent the vice president from having any influence on the outcome.

The law makes clear that Congress should defer to the state’s electoral process and court review, Siegel said, and serve as a backstop only when there are clear and major irregularities, not trivial mistakes and differences of opinion about legal requirements.

Seung Min Kim contributed to this report.