With political winds at his back, Donald Trump on Thursday is expected to use his first speech since surviving an assassination attempt to plead for national unity.

Strategists view the Republican national convention address, likely to be watched by tens of millions of Americans on prime-time television, as a unique opportunity to redefine the former US president as more palatable to moderate voters.

But critics remain sceptical that a Trump reset can last, citing past supposed “pivots” that were hyped by the media only for him to revert to dark, divisive and incendiary outbursts.

“That was a profound existential moment and I’m sure it’s impacted him in the short run, but you are who you are,” David Axelrod, a former chief strategist for President Barack Obama, said. “He isn’t by habit or orientation a unifier.

“Maybe so long as the race is going well others can persuade him that it’s better to be quiet than noisy. But you never know what happens at two in the morning when he’s got his phone in his hand and an impulse in his head.”

As the final night of the convention got underway on Thursday in Milwaukee, opinion polls had Trump, 78, running 11 percentage points ahead of where he was nationally in the 2020 race of the White House. He is surfing a wave of sympathy and adulation after his right ear was injured by a would-be assassin’s bullet at a campaign rally in Pennsylvania on Saturday. Trump received a hero’s welcome at the Republican convention earlier this week from cheering, sign-waving supporters.

Throughout the week, speaker after speaker suggested that Trump’s life was spared by God’s providence so that he can continue a sacred mission for the nation. But they backed away from early accusations that Democrats were to blame for the shooting.

Trump’s running mate, JD Vance, who on Saturday tweeted that the Joe Biden campaign’s rhetoric “led directly” to the attempted assassination, struck a different tone in his convention address on Wednesday night.

“Now consider what they said. They said he was a tyrant. They said he must be stopped at all costs. But how did he respond? He called for national unity, for national calm literally right after an assassin nearly took his life.”

He added: “He is tough – he is – and he cares about people. He can stand defiant against an assassin one moment and call for national healing the next. He is a beloved father and grandfather and, of course, a once in a generation business leader.”

Speakers on Thursday included Mike Pompeo, the former secretary of state, who pumped up the Trump administration’s record. “We put America first every single day,” he said, listing the lack of major new wars, anti-migration policies and “destroying Isis”. Pompeo then joked that Biden only “shuffles” across the global stage, amid a crisis in Biden’s re-election campaign over his age and acuity.

The former Fox News host Tucker Carlson and the retired wrestler Hulk Hogan were also due to take the stage on Thursday.

Melania Trump was expected to appear at the Republican convention on Thursday but, in a break with tradition, would not deliver remarks, according to people familiar with the matter. The former president’s wife has been conspicuously absent in recent months, including from the New York criminal trial where Donald Trump was found guilty of 34 felony counts of falsifying business records.

Some at the convention have shifted their emphasis from “Make America great again” to “Make America one again”. Lara Trump, his daughter-in-law and co-chair of the Republican National Committee, told the convention on Tuesday that Americans should remember “there is more that unites us than divides us”.

In a nod towards moderation, Trump invited his erstwhile Republican rival Nikki Haley to speak. She was greeted with cheers and some boos but quickly quelled the latter by giving Trump a full-throated endorsement. “You don’t have to agree with Trump 100% of the time to vote for him,” she said. “Take it from me.”

In another move aimed at softening Trump’s image, his granddaughter Kai Madison Trump made her debut on the political stage on Wednesday. “He calls me during the middle of the school day to ask how my golf game is going and tells me all about his,” she said. “Grandpa, you are such an inspiration and I love you. The media makes my grandpa look like such a different person but I know who he is.”

Republicans’ show of harmony offers a stunning contrast with Democrats, who have spent weeks mired in intra-party tensions over whether Biden, 81, should abandon his re-election campaign after a hapless debate performance. A national NBC News poll found that just 33% of Democrats are satisfied with Biden as their party’s presidential nominee, versus 71% of Republicans satisfied with Trump.

Speaking at an event in Milwaukee organised by the Cook Political Report and University of Chicago Institute of Politics, Republican pollster and strategist Tony Fabrizio said: “Right now the Democrats are the perfect circular firing squad and, while they’re the perfect circular firing squad, we have the run of the field, and the run of the field for us is to do exactly what we are doing. Running the messaging we are running. The president doing what the president is doing.”

The Trump shooting, and the ensuing national attention, present an opportunity when he formally accepts the party’s nomination to face Biden in a rematch of 2020. His wife Melania and daughter Ivanka, both of whom have been mostly missing from the campaign trail, are expected to attend.

Some Republicans hope Trump can recreate Ronald Reagan’s defiant optimism after he survived an assassination attempt in 1981, casting himself as unifier-in-chief. On Sunday, Trump told the New York Post that he had intended to deliver biting remarks against Biden until the shooting prompted him to throw them out.

Speaking at a CNN-Politico Grill event on the sidelines of the convention on Thursday, Mike Johnson, the speaker of the House of Representatives, said: “I am so looking forward to his address tonight because I think it’s going to be momentous, I think it’s going to be historic, and he’s going to talk about unifying the country, which is why he changed the content of the speech.”

Trump is understood to have been reworking his remarks with his speechwriter Ross Worthington, according to a person close to Trump, and has discussed making himself sound like he is still the president, as opposed to just a candidate.

But at an event hosted by the Axios website, Trump’s eldest son, Donald Trump Jr, suggested that even if Trump shifted to a gentler tone, his core political attacks were likely to continue. “You can be nicer on the margins but you still have to call out insanity when you see insanity,” Trump Jr said when asked about more caustic language turning off potential voters, for instance on transgender issues. “That’s different, that’s not about tone.”

At an event hosted by Georgetown University on the sidelines of the convention, Trump’s co-campaign chief Chris LaCivita acknowledged that the unity messaging would not come at the expense of winning the election in November.

LaCivita said: “This is obviously an opportunity to bring our country together. But let’s not forget we’re in the middle of a campaign. Our focus is very much on putting everything back squarely on the issues that are hurting everyday Americans and providing them an answer to those.”

Indeed, for all the talk of a softer, more inclusive Trump, he has sat in a box in the convention hall alongside extremists such as Carlson, a broadcaster who has promoted white nationalism and praised Vladimir Putin’s Russia, and Marjorie Taylor Greene, the representative who once floated a conspiracy theory involving “Jewish space lasers”.

Many of the speeches in Milwaukee have been centered on the theme of law and order, infused with Trump’s anti-immigrant rhetoric, with speakers angrily denouncing Biden’s southern border policies and referring to an “invasion”. Delegates waved signs that said, “Mass deportation now” and chanted, “Drill, baby, drill!”

There are also some striking absences: the former president George W Bush, the former vice-president Mike Pence and senators Lisa Murkowski (Alaska), Susan Collins (Maine), Todd Young (Indiana), Mitt Romney (Utah) and Rand Paul (Kentucky) are all skipping the convention.

Kurt Bardella, a Democratic strategist, said: He’ll talk about unity and use all the buzzwords for one night but let’s not kids ourselves: it’s an act.”

Joanna Walters contributed reporting