The Senate voted on Friday to override President Donald Trump's veto on the defense spending bill in a rare New Year's Day session.

The stinging rebuke by members of Trump's own party represents the first time in his term that a veto has been overturned.

The vote was 81-13. A supermajority is needed to override a presidential veto.

Sen. Mitt Romney, R-Utah, confirmed today that Mitch McConnell, the Senate majority leader, called the upcoming joint session of Congress on Jan. 6, which will affirm the results of the presidential election, "the most consequential vote" of his lengthy tenure.

"I see that as a statement that he believes it's a -- it's a referendum on our democracy," Romney told reporters.

Sources said that McConnell asked Sen. Josh Hawley, R-Mo., on a New Year's Eve call with Republicans to explain to his colleagues why he is planning to object to the certification of Biden’s electoral win during the joint session. McConnell had privately warned his colleagues weeks ago against doing this as it would put his conference in the position of having to oppose Trump (and thereby his base) publicly.

Hawley, in joining the last-ditch bid by Trump's House allies to overturn the election results, said he objected to states not following their election laws.

"At the very least, Congress should investigate allegations of voter fraud and adopt measures to secure the integrity of our elections," Hawley said in a statement. There has been no evidence of widespread election fraud.

-ABC News' Trish Turner

In a very rare New Year’s Day session, Senate GOP leadership rejected two attempts to debate and vote on the House-passed CASH Act, which would give most Americans $2,000 in direct COVID relief payments. It was an effort by both Sens. Chuck Schumer and Bernie Sanders.

Republicans are continuing to argue that the House bill —- which would allow those making up to $350,000 to receive some cash under the act, albeit a smaller amount than those making less -- amounts to "socialism for the rich."

The chamber’s socialist, Sen. Sanders -- continued to argue that Republicans were “hypocrites” —- blocking this effort but approving big tax breaks for the rich.

He was joined by conservative Sen. Josh Hawley, who slammed the fight by his own leadership.

“With all due respect, this doesn’t seem to be Republicans against Democrats. This seems to be the Senate against United States of America,” said Hawley.

-ABC News' Trish Turner

The Senate is set to cast a preliminary vote this afternoon on overriding President Trump's veto of the National Defense Authorization Act -- which would be the first of his term.

The House voted overwhelmingly earlier this week to override Trump's veto of the $740 billion legislation, which funds the military and that members from both parties have said is vital to both the troops, who get a raise under the measure, and national security.

Trump has called the bill a "gift" to China and Russia.

In vetoing the measure (which has passed every year for 59 years), Trump demanded that Congress include a repeal of Section 230 of the Communications Decency Act, which gives broad legal immunity to tech companies over contents posted by users. He also wanted lawmakers to nix a provision authored by Sen. Elizabeth Warren that requires DOD to rename military bases and installations that honor Confederate generals.

Congress originally passed the measure with veto-proof majorities, and the House recently voted to override the veto. If the Senate votes to override - as it is expected to -- the bill would become law.

Today's test vote (which should be similar - if not identical - to the final vote) is expected to show more than the two-thirds majority required to override Trump's veto.

-ABC News' Trish Turner

The House narrowly passed a bill that would increase the amount of money Americans receive in a second round of pandemic relief stimulus payments to $2,000, up from $600.

The final vote tally was 275-134, receiving the two-thirds majority it required under the expedited vote. There were 44 Republicans who voted with Democrats.

Even though Trump supports the measure, a number of Republicans voted against the bill. Its fate remains uncertain in the Senate.

The House vote comes one day after Trump signed the $2.3 trillion spending and COVID-19 relief bill, which included $600 stimulus checks for Americans who make $75,000 or less. Trump initially threatened to hold up the bill last week and said it was a "disgrace." He spent the next several days calling on Congress to pass a bill that included $2,000 stimulus checks instead.

Democrats took up Trump's offer last week and attempted to pass a bill that would send Americans $2,000 checks via unanimous consent but that attempt failed over Republican objections. House Speaker Nancy Pelosi vowed to bring the bill to the floor for a full recorded vote on Monday.

Even though the bill has now cleared the House, at this point it's unclear if the Republican-led Senate will bring the bill to the floor for a vote. Senate Majority Leader Mitch McConnell made no promises in his statement Sunday when he commended the president for finally signing the COVID-19 relief bill into law.

Pelosi called on Trump to put more pressure on his party to back the payments.

"Every Republican vote against this bill is a vote to deny the financial hardship that families face and to deny the American people the relief they need," she said in a statement released Sunday.

Senate Minority Leader Chuck Schumer said Sunday that he would try to pass the legislation in the Senate.

"No Democrats will object. Will Senate Republicans?" he tweeted.

-ABC News' Mariam Khan