(WASHINGTON) — President Joe Biden stepped up the fight for voting rights on Tuesday, speaking in the nation’s birthplace of Philadelphia and invoking history, saying, “We the People began as a story that’s neither simple nor straightforward.

“But some things in America should be simple and straightforward. Perhaps the most important of those things, the most fundamental of those things is the right to vote, the right to vote freely,” he said in a high-profile speech at the National Constitution Center.

He wasted no time taking a shot at former President Donald Trump and his supporters, homing in on the 2020 election as the “most scrutinized election in American history.

“More than 80 judges, including those appointed by my predecessor heard the arguments. In every case, neither cause nor evidence was found to undermine the national achievement of administering the historic election,” he said.

“The big lie is just that — a big lie!” he declared.

“In America, if you lose, accept the results. Follow the Constitution. Try again. You don’t call facts fake and try to bring down the American experiment just because you’re unhappy,” he continued. “That’s not statesmanship — that’s selfishness.”

He called passing national voting legislation “a national imperative.”

“Republicans opposed even debating, even considering the For the People Act. Senate Democrats stood united to protect our democracy and the sanctity of the vote. We must pass the For the People Act,” Biden said to applause.

Biden also raised the Jan. 6 attack on the Capitol as a dangerous and unprecedented consequence of Trump’s “big lie” about the 2020 election.

“Because of the extraordinary courage of elections officials, many of them Republicans, our court system, those brave Capitol Police officers — because of them — democracy held. Look how close it came,” he continued. “We’re going to face another test in 2022 new wave of voter suppression and raw and sustained election subversion. We have to prepare now.”

He later said the even Confederate soldiers didn’t breach the Capitol and that “we’re facing the most significant test of our democracy since the Civil War.”

“So, hear me clearly: There is an unfolding assault taking place in America today, an attempt to express and subvert the right to vote in fair and free elections. An assault on democracy, an assault on liberty, an assault on who we are as Americans,” he said.

His use of the bully pulpit comes as his administration wades more aggressively into the fight over ballot access at the urging of civil rights groups and Democrats as Republican-led legislatures advance new voting restrictions in places like Texas and Congress remains deadlocked over proposed legislation.

It also comes as Democrats in the Texas State Legislature have fled their state for Washington, D.C., the second such effort in recent weeks in an attempt to prevent a vote on legislation they say will roll back voting rights in the state.

The state lawmakers said in a press conference earlier Tuesday outside the Capitol that they’re there to pressure Congress to pass federal voting rights legislation and call for an exception to the Senate’s filibuster rule blocking Democrats from moving forward with a measure, they say, would stop GOP-led efforts to restrict voting in Texas and nationwide.

In March, House Democrats advanced the For the People Act, an expansive package that would transform federal elections, voting and congressional redistricting — but it has stalled in the Senate after failing to advance in a procedural vote late last month, over opposition from all Republicans.

In light of the GOP opposition, Democrats have pushed for the Senate to reform the legislative filibuster, with House Democratic Whip Jim Clyburn, D-S.C., a key Biden ally and endorser during the 2020 Democratic primary, suggesting Democrats create an exception to the 60-vote threshold for election reform and other constitutional issues. Because of their opposition to ending the filibuster, Democratic Sens. Joe Manchin of West Virginia and Kyrsten Sinema of Arizona play a pivotal role in the ongoing congressional negotiations over a national voting rights bill.

Biden did not directly mention Manchin, Sinema or the filibuster in his remarks Tuesday.

Sixteen states have enacted 28 laws that would restrict voting access, out of hundreds that have been introduced throughout the country, according to the Brennan Center for Justice at NYU School of Law.

ABC News’ Alisa Wiersema and Libby Cathey contributed to this report.

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