WASHINGTON 

US Vice President Mike Pence rejected outgoing President Donald Trump's demand Wednesday that he interferes in Congress's counting of Electoral College votes, just minutes before lawmakers were set to convene in a rare joint session.

The largely pro forma meeting will eventually declare President-elect Joe Biden the winner of the presidential contest, although it will be significantly prolonged as some Republicans in the House of Representatives and the Senate have begun to raise objections.

Trump asked Pence, who holds a largely ceremonial role in Wednesday's proceedings, to reject electors from key battleground states he lost in a last-ditch effort to overturn the will of voters who cast 7 million more ballots for Biden on Nov. 3. 

Pence said in a letter to Congress that he cannot claim "unilateral authority" to decide America's next commander-in-chief, but vowed to hear objections raised by lawmakers. 

"Our Founders were deeply skeptical of concentrations of power and created a Republic based on separation of powers and checks and balances under the Constitution," he wrote. "Vesting the vice president with unilateral authority to decide presidential contests would be deeply antithetical to that design."

The letter was distributed minutes after Trump told supporters at a rally near the National Mall that he would be "very disappointed" if the hitherto loyalist vice president did not heed his demands. 

“Mike Pence I hope you’re going to stand up for the good of our Constitution, and for the good of our country, and if you’re not I’m going to be very disappointed in you. I will tell you right now. I am not hearing good stories,” he said during his speech. 

He later expressed his disappointment with Pence on Twitter, saying he did not show courage.

Trump continued to tout his claims of voter fraud, energizing his supporters, even as those claims have been repeatedly rejected in legal proceedings, and federal probes have failed to deliver evidence. Top elections officials, including Republicans, have also denied their authenticity, at times issuing stern rebukes. 

Trump said he would lead protesters to the Capitol to contest the proceedings. It is unclear if he followed through on his rhetoric, but video captured from the Capitol and posted on social media showed riot-like scenes of Trump's supporters clashing with police as they attempted to breach the legislature.