ATLANTA - Pounding his fist for emphasis, President Joe Biden challenged senators on Tuesday to “stand against voter suppression,” urging them to change Senate rules in order to pass voting rights legislation that Republicans are blocking from debate and votes.

Biden told a crowd in Atlanta that he'd been having quiet conversations with senators for months over the two bills - a lack of progress that has brought his criticism from activists in his own party.

“I’m tired of being quiet!" he shouted. “I will not yield. I will not flinch.”

Current rules require 60 votes to advance most legislation - a threshold that Senate Democrats can’t meet alone because they only have a 50-50 majority with Vice President Kamala Harris to break ties. Republicans unanimously oppose the voting rights measures.

Not all Democrats are on board with changing the filibuster rules. Conservative West Virginia Sen. Joe Manchin threw cold water on the idea Tuesday, saying he believes any changes should be made with substantial Republican buy-in.

And even if Democrats clear the obstacles to passage of the voting rights laws, it could be too late to counter widespread voting restrictions passed in 19 states following former President Donald Trump’s 2020 loss and his lies - embraced by many in the GOP -- that the election was stolen through voter fraud.

“This matters to all of us," he insisted. "The goal of the former president and his allies is to disenfranchise anyone who votes against him, simple as that.”

Biden spent decades in the Senate, and he spoke of how much it’s changed for the worse, calling it “a shell of its former self. It gives me no satisfaction to say that as an institutionalist.” He spoke of an era not long ago when an issue like voting rights would never have been so rancorously partisan.

He recalled working with notorious segregationist lawmakers in the Senate to get legislation passed and for it then to be signed into law by Republican presidents. But now, the filibuster has been used rampantly to block even the debating of some legislation.

With Senate Majority Leader Chuck Schumer, D-N.Y., setting next Monday’s Martin Luther King Jr. Day as a deadline to either pass voting legislation or consider revising the rules around the chamber’s filibuster blocking device, Biden is expected to evoke the memories of the U.S. Capitol riot a year ago in more forcefully aligning himself with the voting rights effort.

Biden told his audience: “The next few days, when these bills come to a vote, will mark a turning point in this nation.”

“Will we choose democracy over autocracy, light over shadow, justice over injustice? I know where I stand. I will not yield. I will not flinch,” he declared. “I will defend your right to vote and our democracy against all enemies foreign, yes and domestic! And so the question is where will the institution of the United States Senate stand?”

Biden on Tuesday also paid tribute to civil rights battles past - visiting Atlanta's historic Ebenezer Baptist Church, where the late Rev. Martin Luther King Jr. once held forth from the pulpit. He stood quietly as Martin Luther King III placed a wreath outside at the crypt of King and his wife, Coretta Scott King. And he referenced civil rights battles of the 1960s in his animated speech on the grounds of Morehouse College and Clark Atlanta University.

Vice President Kamala Harris spoke before Biden Tuesday, warning that a barrage of laws making it tougher to vote means there is “a danger of becoming accustomed to these laws, a danger of adjusting to these laws as though they are normal.”

“There is nothing normal about a law that makes it illegal to pass out water or food to people standing in long voter laws,” she said, to cheers.

Some voting rights advocates boycotted Biden's speech. Georgia Democratic gubernatorial candidate Stacey Abrams, known for her untiring voting rights work, also was skipping the event. The White House, meanwhile, sent out an unusually long list of attendees for the speech. Aides said Abrams had a conflict but didn’t explain further, though she tweeted support for the president.

Biden said before his trip the two had a scheduling mix-up but had spoken and were “all on the same page.”

When asked what he was risking politically by speaking out when there aren't enough votes to change the rules, he said: “I risk not saying what I believe. That’s what I risk. This is one of those defining moments. It really is. People are going to be judged on where were they before and where were they after the vote. History is going to judge us."

Voting rights advocates in Georgia and nationwide are increasingly anxious about what may happen in 2022 and beyond. They view the changes in many states as a subtler form of ballot restrictions like literacy tests and poll taxes once used to disenfranchise Black voters, a key Democratic constituency.

Republicans who have fallen in line behind Trump’s election misinformation are separately promoting efforts to influence future elections by installing sympathetic leaders in local election posts and by backing for elective office some of those who participated in the riot at the U.S. Capitol a year ago.

Democratic Sen. Raphael Warnock of Georgia, who is senior pastor at Ebenezer Baptist and made history as the first Black senator elected in Georgia, said that “anything that can happen that will continue to shine a bright light on the urgency of this issue is important.”

Georgia is at the center of it all, one of the key battleground states in the 2020 elections. After the votes were counted and recounted, Trump told a top state election official he wanted the official to “find” enough votes to overturn his loss. The state’s votes nonetheless went to Biden, and both of its Senate seats went to Democrats as well.

Last year, the Republican governor signed a sweeping rewrite of election rules that, among other things, gives the State Election Board new powers to intervene in county election offices and to remove and replace local election officials. That has led to concerns that the Republican-controlled state board could exert more influence over the administration of elections, including the certification of county results.

Congressional Democrats have written voting legislation that would usher in the biggest overhaul of U.S. elections in a generation by striking down hurdles to voting enacted in the name of election security, reducing the influence of big money in politics and limiting partisan influence over the drawing of congressional districts.

The package would create national election standards that would trump state-level GOP laws. It would also restore the ability of the Justice Department to police election laws in states with a history of discrimination.

By ALEXANDRA JAFFE, COLLEEN LONG and JEFF AMY