The 2024 election campaign has a new iconic image: Donald Trump, moments after narrowly avoiding serious injury or death from an assassin’s bullets, standing with his fist raised, lines of blood streaked across his face, an American flag billowing in the breeze behind him.

“Fight! Fight! Fight!” the former president said, as some of the supporters, who moments before had feared for their lives, began cheering.

The bloodshed in Pennsylvania will leave a lasting mark on the American psyche, puncturing the veneer of security around the highest levels of presidential politics – of magnetic screening, bulletproof limousines and heavily armed Secret Service agents. Even former presidents are not insulated from the violence that can erupt in everyday American life.

It was also a dramatic moment in American political history; one that is sure to be replayed in video clips, still photographs and testimonial accounts throughout the course of this presidential campaign and in campaigns to come.

In a rare address from the Oval Office Sunday evening, President Joe Biden called on Americans to cool the temperature around political debate.

“[It] must never be a battlefield and, God forbid, a killing field,” he warned. “No matter how strong our convictions, we must never descend into violence.”

The attack has already begun coursing through America’s partisan dialogue, as numerous Republicans have spoken out to condemn President Biden and the Democrats for creating a rhetorical environment conducive to the violence.

They point to dire warnings about the former president becoming a dictator and threatening democracy as examples of the overheated language that could inspire an assassin.

In particular, they highlight leaked comments the president made in private to donors just last week about increasing the attacks on the former president’s record and putting a “bull’s-eye” on him.

“They’ve tried to take him out in so many other ways, financially, they’ve tried to throw him in jail,” Donald Trump Jr said in a television interview on Sunday. “It’s almost as if they would love for this to happen.”

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At least so far, however, the motives and political affiliations of the alleged assassin, 20-year-old Pennsylvania resident Thomas Matthew Crook, are in doubt. They may ultimately defy an easy partisan narrative.

The former president’s oldest son went on to add that, after the assassination attempt, those on the left can no longer accuse the former president of culpability for the 6 January attack on the US Capitol.

That violent episode took place hours after the then-president had held a rally just a few dozen blocks away, challenging the 2020 election results. His actions on that day led to his impeachment by the House of Representatives and, more than a year later, indictment by a special counsel appointed by the US attorney general.

If the Pennsylvania shooting defuses this line of criticism by Democrats, it’s just one way in which it will have fundamentally reshaped this presidential campaign. Others may become clear over the course of the Republican National Convention, which starts on Monday in Milwaukee.

The failed attack on the former president plays into several themes the Trump campaign was already planning for the quadrennial gathering, which culminates with Trump taking the stage to accept his party’s nomination on Thursday night.

The first is that it could provide a boost to the politics of grievance and persecution that have been a central focus of his rally speeches and social media posts.

“They’re not really after me; they’re after you,” is a common Trump refrain, on t-shirts, billboards and car stickers. “I’m just in the way.”

That message will land with new force after the former president and his crowd of supporters were sprayed with bullets. Trump’s legions of fans – many of whose support borders on near-messianic hero-worship – will have all the more reason to identify with a man who almost lost his life while standing before them.

The former president’s brush with death, and subsequent acts of bloody defiance, will also fit with the contrast Trump campaign officials have said they are trying to draw at this week’s convention – one where their candidate, and party, embody rugged masculinity and strength, while their opponents are feeble.

President Biden’s age and capabilities have dogged his campaign for months – and prompted a Democratic crisis of confidence in his re-election effort after a stunningly poor performance at the presidential debate just over two weeks ago.

Saturday night’s attack, and Trump’s response to it, will allow Republicans to put that contrast in stark relief in the days ahead.

Democrats have spent the past two weeks in anguished soul-searching over their president’s political future. Now, they have a new set of concerns.

In a way, the assassination attempt may end up providing a political lifeline to Mr Biden, given that the focus has dramatically shifted away from his age-related struggles and internal attempts to oust him. But the president’s re-election strategy – which hinges on painting Trump as a danger to the nation if he again becomes president – could be seriously hampered if the American public is hostile to new, pointed criticisms of the man.

The Biden campaign has already pulled all negative advertising directed at the former president, lest it be viewed as inappropriate given the national mood. The president also rescheduled a trip to Texas planned for Monday.

It is only a pause, however, and Democrats will need to go back on the offensive if they hope to erase the narrow lead the former president holds.

That lead – small and not insurmountable, but still significant – has held stable for months, even as national politics have been buffeted by a seemingly endless stream of unprecedented news stories.

The former president’s trial and conviction, a series of landmark Supreme Court decisions, Mr Biden’s debate flop – none of these has seemed to move the American political needle in what has been, and appears destined to remain, a sharply divided nation.

While there has been considerable talk about how this presidential campaign has been upended by the assassination attempt, there is no guarantee that the race will not return to its near-dead-heat equilibrium point in the three months before election day.

Only now the Democrats have less time, less of a money advantage and less political oxygen to shift the electoral dynamics in their favour.

What Saturday night’s tragedy demonstrated most clearly, however, is that expectations and political narratives can shift in seconds.