US President Joe Biden hit the campaign trail on Tuesday for the first time since the assassination attempt against Donald Trump, seeking to prop up his re-election bid as unease over his age resurfaces.As Trump rides a wave of support at the Republican National Convention in Milwaukee, Biden is in Las Vegas to reach out to Black voters at the NAACP advocacy group.The 81-year-old president will also sit down with Black broadcaster BET, the latest in a series of interviews as he tries to address concerns over his mental fitness following his dismal debate performance against Trump last month.Amid his call for Americans to “lower the temperature” of politics in the wake of the attempt on Trump’s life, Biden cancelled a campaign trip to Texas on Monday but continued with his Nevada visit.Biden narrowly won Nevada in his 2020 election victory over Trump. The trip comes as the Democratic Party pushes ahead with plans to rush through Biden’s own nomination ahead of its conference in August, despite calls to postpone the process while divisions remain over his candidacy.While the attempt on Trump’s life briefly silenced Democrats who called on Biden to step aside, tensions are emerging in public again as president trails in most the polls. The New York Times reported that a group of Democrats in the House of Representatives was trying to rally support for a change to the rules to allow challenges at the convention.But Biden’s campaign insisted the virtual roll-call was necessary before the August 19 convention as Republican-led Ohio had moved its filing date to August 7, otherwise Biden risked not being eligible there. “It is our obligation as a campaign to make sure that President Biden is on the ballot,” Biden deputy campaign manager Quentin Fulks told a press conference in Milwaukee.At the NAACP meeting in Las Vegas, there was widespread support for Biden staying on.“We’re riding with Biden,” said Sydney Martin, 65, assistant pastor of the Destiny House Christian Center in New York state, describing calls for Biden to step aside as a “trick by the enemy.”Asha Holmes, 28, said she would also back Biden although she had been “kind of hoping for Kamala (Harris, the vice-president) to try and run this year instead of him going for a second term.”But the questions continue about whether Biden can win again after a faltering showing at the Atlanta debate on June 27 where he mangled his words and lost his train of thought.Biden, who says he messed up due to jet lag and illness, forcefully defended his ability to do the job in a major US network interview on Monday night.“I’m old,” Biden told NBC. “But I’m only three years older than Trump, number one. And number two, my mental acuity has been pretty damn good.”Biden also defended his rhetoric about Trump after Republicans accused him of stoking divisions ahead of the shooting in which the former president’s ear was hit.FBI investigators are still probing 20-year-old gunman Thomas Matthew Crooks’ motivation for the attack on a Trump rally in Butler, Pennsylvania. A bystander was killed and Crooks was shot dead.Biden admitted it was a “mistake” to tell donors in a call last week that it was “time to put Trump in the bullseye” of his election campaign.But Biden doubled down on what he said was the need to “talk about the threat to democracy” posed by former president Trump.Trump refuses to accept the 2020 election results and faces criminal charges over the deadly January 6, 2021 assault on the US Capitol by supporters seeking to overturn his defeat by Biden.