There were a lot of things in Tim Walz’s favour to propel him on to the Democratic ticket as the pick for VP. A former teacher, former football coach and salt-of-the-earth Nebraskan with a history of flipping strong Republican seats, Walz looks like the kind of guy who would stop to tow your car out of a ditch, even if it were carrying a Donald Trump bumper sticker. He has a degree from a modest state college. He has served in the military. And yet, one suspects, the single detail that won the 60-year-old the job was his emperor’s clothes use of the word “weird”. On Tuesday, Walz appeared in Philadelphia alongside Kamala Harris in their first joint appearance and – apart from the mind-blowing revelation that Walz, who looks as if he might have served in Vietnam, is approximately the same age as Harris – two things became immediately clear. That the governor of Minnesota has the ease and charm of a natural politician that Harris, on a bad day, can lack. And that he will present his Republican counterpart, JD Vance, with a gratifyingly large problem. That problem is authenticity, one of the major absurdist planks of Trump’s campaign, in which the scion of a New York real estate empire accuses his rivals of being “east-coast elites”. Walz, unlike almost every other high-profile Democrat going back decades – including Hillary Clinton’s affable and somewhat Walz-like 2016 running mate, Tim Kaine – is not a lawyer. He did not go to Harvard or Yale, a fact he is proving happy to weaponise. If Walz has the energy of a dad reminding his grown-up kids to stay hydrated, he is also, on the evidence of the first day of campaigning, still very much the high school coach running the cafeteria at lunchtime, using all the modes – sarcasm, booming aggression, sudden, sharp mockery – that traditionally keep feral adolescents in order. To wit: grinning wolfishly, Walz said to the crowd in Philadelphia: “Like all regular people in America’s heartland, JD Vance studied at Yale, had his career funded by Silicon Valley billionaires, and wrote a bestseller trashing that community … COME ON!”, a line he tweeted the next day for anyone who missed it. As the New Yorker noted this week, when Walz joined the recent White Dudes for Harris video fundraiser, he went ahead and said the quiet part out loud, observing in reference to Trump, “How often in the world do you make that bastard wake up afterward and know that a Black woman kicked his ass, sent him on the road?” The brilliant thing about Walz’s use of the word “weird” is that it cuts through years of Democrats getting in their own way trying to find clever ways to shame Trump. Walz’s attack observes a rule once delineated by Tony Blair; that in politics you get nowhere by calling your opponent a “fascist”, and everywhere by using small, personal insults that tend to stick. Trump, with his playground bully mentality, understands this better than anyone, which is why over the years he has successfully ridiculed Marco Rubio for his height, Ted Cruz for his silly fibbing, and Elizabeth Warren for her ill-judged claim to be part Native American. Now Walz and Harris, doubling down on “weird” with the equally useful “creepy”, are among the Democrats who have finally caught on. There are still huge numbers of anxieties. Vance will go after Walz for his delayed response to the Minneapolis riots that broke out after a police officer murdered George Floyd in 2020. Israel remains a source of rancour and division among Democrats that will cost the Harris-Walz ticket votes. And in the hours after Walz’s candidacy was announced, while fundraising surged, many prominent Democrats in Hollywood stepped forward to applaud him, with the usual souring effect. Let’s hope enthusiasm for Walz survives the proselytising of John Cusack and Cynthia Nixon, two people you would go considerably out of your way to avoid attracting endorsement from, in particular Nixon, who once mounted a whimsical bid to be governor of New York. As we speak, we must assume that George Clooney’s assistant is putting the finishing touches on a piece to run under the actor’s byline in the New York Times op-ed page next week. Still, the excitement and growing momentum of Harris’s ascendance seems, this week, to have been only boosted by Walz, who on first impressions looks like a smart pick. Instead of the Catholic astronaut, the Jewish-American governor who might have delivered Pennsylvania, and the matinee idol governor of California, Harris chose the man one can imagine enjoying a branch of Home Depot while honing his successful and accessible leftwing agenda. Emma Brockes is a Guardian columnist