Washington CNN  — 

President Joe Biden issued blunt new warnings about ongoing existential threats to US democracy in a major address Thursday, sharpening the central argument in his potential rematch with Donald Trump and asking voters to prioritize the health of American institutions.

“There’s something dangerous happening in America now,” Biden said during his speech in Arizona, where he was also honoring his friend, the late Republican Sen. John McCain. “There’s an extremist movement that does not share the basic beliefs of our democracy: The MAGA movement.”

“There’s no question that today’s Republican Party is driven and intimidated by MAGA Republican extremists,” he said, using the acronym for Trump’s political movement. “Their extreme agenda, if carried out, would fundamentally alter the institutions of American democracy as we know it.”

The stark message was Biden’s most forceful attempt at calling out Trump’s antidemocratic behavior since the former president was criminally charged for his attempts to subvert the 2020 election results. It offered a taste of Biden’s forthcoming reelection message, one centered on Trump’s own words and actions as threats to democracy. Biden said his predecessor was guided not by the Constitution or decency, but by “vengeance and vindictiveness.”

As indictments and arrests of the former president piled up over the summer, Biden remained mostly silent on his predecessor, wary of appearing to intervene in Justice Department business. His most substantive comment on Trump’s myriad legal issues was a sarcastic remark about his mugshot in the Fulton County, Georgia, case.

But as Trump’s prohibitive lead in the Republican primary remains unchanged – and as Biden’s own standing remains mired in low approval – the president is sharpening his attacks on his most likely 2024 rival as a danger to democracy. Thursday’s speech served as yet another sign that the days of trying to keep Trump at an arm’s length are long gone.

“Trump says the Constitution gave him the right to do whatever he wants as president,” Biden said, referencing his most likely GOP challenger by name. “I’ve never heard presidents say that in jest.”

He alluded to Trump’s recent suggestion that Gen. Mark Milley, the chairman of the Joint Chiefs of Staff, could be executed, and said Republican silence on the comment was “deafening.”

Stopping the erosion of democratic institutions and values was central to Biden’s decision to run for president in 2020, it will again be core to his reelection campaign, officials said, as he looks to energize voters and donors who have otherwise appeared lukewarm about a rematch between the two men.

“We should all remember: Democracies don’t have to die at the end of a rifle. They can die when people are silent, when they fail to stand up,” Biden said.

Senior Biden advisers had mulled over the timing and location of Thursday’s speech for weeks. Previously, Biden has sought to harness the symbolic settings of Independence Hall and Gettysburg to issue warnings about the state of American democracy.

Advisers eyed similar sites pegged to American history on the East Coast before settling on Tempe, Arizona, in part as a way to honor the late Republican Sen. John McCain, whom Biden was friends with for decades and referred to as a “brother.” Biden announced funding to construct the McCain Library, honoring his longtime friend.

Arizona was also a center of Trump’s efforts to overturn the 2020 election results, and a state where voters rejected candidates who denied the results two years later. That effort loomed large in the president’s message.

“I believe in free and fair elections and peaceful transfer of power. I believe there’s no place in America – none, none, none – for political violence,” Biden said.

Biden’s advisers also selected the day after the second Republican primary debate, hoping to insert Biden into a news cycle otherwise dominated by the GOP contest. Trump skipped the debate, delivering a speech in Michigan instead as he looks to cut into Biden’s support among union workers.

The speech came at a moment of political uncertainty for Biden, as he faces persistent questions about his age, disapproval of his handling of the job and an indictment of his son, Hunter. House Republicans held their first hearing in an impeachment inquiry into Biden on Thursday.

Many senior Democrats believe once voters come to see the 2024 election as a contest between Biden and Trump, the stakes will be clearer and the current president’s standing will improve.

At one point in his speech, Biden was interrupted by climate activists as he urged the audience to “put partisanship aside, put country first.” Kai Newkirk, one of the protesters, had stood up and called on Biden to take further action to address fossil fuels.

“I tell you what, if you shush up, I’ll meet with you immediately after this,” Biden said, before resuming remarks.

“Democracy is never easy – as we just demonstrated,” he joked.

Newkirk added in a statement later Thursday that he did not hear the president’s offer to meet with him but that he would have “gladly” accepted.

“I worked hard to elect President Biden, and conscience compelled me to interrupt his speech today to ask why he has yet to declare a climate emergency,” he said in a post on X.

Top Biden donors, many of whom have agitated for more forceful attacks on Trump at this early stage in the campaign, were informed of the plans for Thursday’s speech by senior Biden advisers during a fundraising retreat in Chicago earlier this month. Biden began previewing his address to donors behind closed doors last week.

In those remarks, Biden debuted new warnings about his predecessor’s potential return to the White House, testing the material off-camera as he and his team were preparing for Thursday’s address.

“Let there be no question: Donald Trump and his MAGA Republicans are determined to destroy American democracy. And I will always defend, protect, and fight for our democracy. That’s why I running,” he said at a Broadway theater last week.

Two days later, he amplified his warnings to a group of lawyers – and said he was confident he could defeat Trump for a second time.

“I’m now running again. Because guess what? I think that it’s likely to be the same fellow, and it’s likely that I think I can beat him again,” he said.

Defending democracy is an issue Biden allies believe remains deeply resonant with voters, almost three years after the 2020 contest. The video announcing his reelection opened with footage of the January 6, 2021, attack on the US Capitol.

In the lead-up to the 2022 midterm elections, Biden delivered a resounding message in front of Philadelphia’s Independence Hall, warning of “MAGA forces” that “tried everything last time to nullify the votes of 81 million people.” Ahead of the speech, Biden convened his communications staff with a group of academics and historians – including Pulitzer Prize-winning author Jon Meacham, who has helped draft his highest-profile addresses – to reflect on the fragile state of the union and compile ideas.

The White House remains in touch with several of those historians to continue generating ideas, according to officials.

Democrats say the message worked. The administration and national Democrats have touted the results of the 2022 midterm elections, and the fact that a so-called red wave never materialized as many had predicted, as proof the president’s focus on themes like defending democracy struck a chord.

Thursday’s remarks were billed by the White House as the president’s fourth major speech on the theme of democracy – Biden spoke to the issue last year to mark the one-year anniversary of the January 6 insurrection, as well as days before the midterm elections.

By also honoring McCain during his speech Thursday, Biden hoped to harken to an era of bipartisanship in Washington that has disappeared in recent years. The comparison is amplified given the current battle over government funding, which appears destined to result in a government shutdown by the end of the week.

He was joined at the speech by McCain’s widow Cindy, other members of the McCain family and Democratic Gov. Katie Hobbs.

However, one of the state’s senators, Kyrsten Sinema – who was a Democrat until she left the party last year to become an independent – said Biden should use his visit to Arizona to observe the situation at the southern border.

“It’s well past time for President Biden to see the border crisis first hand and for the administration to do its job, secure the border, and keep Arizona safe. While he’s in Arizona, I’m calling on him to visit the border to actually understand how our communities shoulder the burden of his administration’s failure to address this crisis,” she said in a statement.

McCain’s death was deeply personal and painful for Biden for a number of reasons, including the fact that McCain had been diagnosed with the same cancer that took the life of Biden’s son, Beau. After laying a wreath near the site where McCain’s plane was shot down in Hanoi this month, Biden said he missed his former Senate colleague.

“He was a good friend,” Biden said.

In his eulogy for McCain in the summer of 2018, Biden described his friend as having “lived by a different code – an ancient, antiquated code where honor, courage, integrity, duty were alive.”

This story has been updated with additional information.

CNN’s Jeremy Diamond contributed to this report.