On Wednesday, the U.S. House and the Senate will assemble in a joint session to count the electoral college votes, as the Constitution requires. The session is typically heavy on ceremony and light on drama, despite an occasional protest over the electoral votes.

But very little about Donald Trump’s presidency has been typical, and this apparently won’t be, either. Trump has turned the normally perfunctory session into a loyalty test, urging Republicans to throw out certified votes and overturn the election of Joe Biden and Kamala D. Harris as president and vice president, respectively. Trump’s unfounded allegations of voter fraud have been rejected by dozens of state and federal courts, including the Supreme Court. An effort by some House Republicans to force Vice President Pence to reverse Trump’s electoral defeat also failed in federal court. Even so, many House Republicans plan to object during the joint session, joined by at least a dozen Senate Republicans.

Four authorities set procedures for counting — and contesting — electoral college votes: the Constitution, the Electoral Count Act of 1887 (enacted in the wake of the contested presidential election of 1876), relevant congressional precedents from past joint sessions and a congressional resolution to guide the joint session proceedings. These rules will make it extremely difficult to overturn the electoral college’s results and will tightly circumscribe the discretion of the vice president, who typically presides over the joint session. Trump’s allies can drag out the process, but most expect that the joint session will eventually affirm the election of Biden and Harris.

Here’s what you need to know about the road ahead.

Lawmakers count votes; they don’t certify them.

The 12th Amendment boils down proceedings this way. The vice president, serving as the president of the Senate, “shall, in the presence of the Senate and House of Representatives, open all the certificates and the votes shall then be counted.” The Electoral Count Act fleshes out details, including directing “tellers” — House and Senate members selected before the joint session by their respective chambers — to count the votes.

The vice president opens ballot envelopes from the states in alphabetical order. For each state, the vice president shares the papers with the tellers, who read them aloud. The vice president asks whether any member of Congress wishes to raise an objection. Neither law nor past practice stipulates what counts as a valid objection, but the law makes plain that objections must be in writing and signed by at least one member from each of the chambers.

If a House and Senate member lodges an objection, legislators withdraw to their respective chambers. The law provides for two hours of debate on the objection before each chamber votes. It takes simple majorities of both chambers to reject a state’s electoral votes. Given a House controlled by the Democrats, it’s highly unlikely that the two chambers would agree to reject state-certified votes.

Whatever the outcome, lawmakers then reassemble in joint session for the tellers to announce the results. If there were no objections, the tellers record and count each state’s votes and move on to the next state. After the tellers count and record votes from all 50 states and the District of Columbia, the vice president declares whether any candidates have received the requisite majority votes. That announcement finalizes the election.

What about rival electoral slates?

Trump partisans could disrupt the count in other ways by exploiting some of the electoral law’s ambiguities. For instance, the law plainly requires the vice president to hand the tellers not only all state-certified electoral votes, but also all “papers purporting to be certificates of the electoral votes.”

What counts as a purported certificate? In Arizona, for example — Biden won the state’s 11 electoral votes — 11 Republicans sent a notarized document with a facsimile of the state seal to the National Archives, asserting that the state delivered its votes to Trump and Pence. Must that be handed over? Law and congressional precedents say nothing about what qualifies as a “purported” certificate. But the Electoral Count Act does favor counting slates certified by state governors by the law’s “safe harbor” date, which last year came Dec. 8.

But neither law nor precedent grants the vice president any discretion about which ballots to hand to the tellers, whether from Arizona or other states where Trump loyalists might create papers that “purport” to be certificates. Conceivably, Pence could hand the tellers all such papers sent in by GOP groups, enabling him to evade Trump partisans’ anger and forcing both chambers to muster majorities to go on record voting to reject rogue slates.

These old rules are hard to break

These or other protests — such as the push by a dozen GOP senators to delay the count until after an emergency 10-day audit of the president’s debunked claims of electoral fraud — are highly unlikely to succeed. Simply put, the rules of the game put the burden on challengers to secure bicameral agreement to toss valid votes. With split party control of the chambers and a divided GOP majority, Trump and his allies’ norm-breaking refusal to accept the electoral results are all but bound to fail — even if they succeed in stoking GOP voter distrust of the Biden-Harris win.

Granted, legal scholars have gamed out other potential scenarios should opponents gain traction with their challenges. More likely, Biden and Harris will eventually advance to the White House.