In picking Tim Walz as her running mate, Kamala Harris is signalling confidence

Democratic presidential candidate Kamala Harris holds a campaign rally with her new running mate, Tim Walz, in Philadelphia. EPA

In selecting Minnesota governor Tim Walz as her running mate, US Vice President Kamala Harris is strongly signaling confidence and a broad, rather than region-specific, campaign strategy aimed at the whole country. It reportedly came down to Mr Walz or Pennsylvania governor Joshua Shapiro. Apparently she went with personal chemistry and midwestern homespun rhetorical power over the mathematics of a potentially narrow victory.

If Ms Harris were primarily focused on clawing her way to a winning 270 votes in the electoral college, she surely would have selected Mr Shapiro. He's the extremely popular governor of Pennsylvania, a state she cannot afford to lose. Polls show Pennsylvania currently running as a dead heat between Ms Harris and her Republican opponent, former president and convicted felon Donald Trump. Picking Mr Shapiro would have been a sounder choice if Ms Harris were nervous about the outcome.

Her decision suggests she's not.

Arguments against Mr Shapiro included his outspoken condemnation of anti-Gaza war protesters and unwavering support of Israel (although not Israeli Prime Minister Benjamin Netanyahu). Alarm about this on the left was overblown, because, as vice president, he would have no policy role on Israel and the Palestinians, and would perforce support Ms Harris's policies.

Walz began branding Maga leaders, particularly Trump and his running mate, JD Vance, as just 'weird'

But foregoing the potential advantage he might supply in Pennsylvania also avoids reopening now largely healed wounds over US President Joe Biden's strong support for Israel's brutal Gaza war, especially in its first few months. Within their administration, Ms Harris took the lead in calling for ceasefires and expressing concern about the desperate plight of Palestinian civilians facing Israel's terrible vengeance. Selecting Mr Shapiro might have unduly reopened an internal Democratic controversy best postponed until after November at the earliest.

She could come to regret the choice. Mr Shapiro is known for his polished public speaking, strikingly reminiscent in tone and style to former president Barack Obama.

Pennsylvania Governor Josh Shapiro during a campaign rally for Kamala Harris and Tim Walz in Philadelphia, Pennsylvania. AFP

Nonetheless, Mr Walz was also almost certainly selected for his own, very different, messaging ability. After a long career in the military and education, the House of Representatives, and two terms as Minnesota governor, he has perfected a traditional but now rare brand of distinctly liberal "prairie populism".

He often looks like he just climbed down from a tractor, and employs a plainspoken, unadorned yet powerful verbiage honed in farmhouses, diners and truck stops across the American Midwest. If he can’t get through to winnable heartland independents and Republicans, maybe no one can.

Although long-favoured by Democratic centre-leftists and progressives, Mr Walz shot to national prominence in recent weeks by pioneering a novel yet effective Democratic attack on Mr Trump and his followers. He recently began branding Maga movement leaders, particularly Mr Trump and his running mate, senator JD Vance, as just “weird".

In one simple word, he managed to distill the gut feeling most Democrats and many other Americans have towards Trump-inflected Republican extremists (a reaction not provoked by traditional Republicans): that they are downright strange folk whose conduct, values, and apparent mental landscape often seem inexplicable.

Donald Trump with running mate Senator JD Vance. Mr Trump recently said vice presidential candidates don't matter. Bloomberg

Why did Mr Trump go to a convention of black journalists and aggressively launch a sustained barrage of obviously racist attacks on the moderators, and against Ms Harris’s ethnicity, apparently unable to comprehend that someone can be both black and Indian due to mixed parentage?

For a candidate professedly seeking greater support from African Americans, the performance, yet again, struck most Democrats as simply weird. So do his incoherent stories about sharks and electricity, self-indicting poems about treacherous snakes, and many other greatest hits.

Why did Mr Trump then, in his own must-win state of Georgia, unleash a tirade of abuse against popular governor Brian Kemp and even his wife? And why does Mr Vance refuse to moderate or amend his offensive and misogynistic charge that the US is being brought to ruin because it's run by "childless cat ladies"?

The whole cult of personality surrounding Mr Trump in the Republican Party is unprecedented in modern American history and, to Democrats, certainly appears very "weird”.

Mr Walz is, in part, being rewarded for pioneering this extremely effective attack. However, Democrats must be careful. Many within their own ranks could be plausibly cast as "weird" to a broad swathe of American voters, including the ultra-left, extreme environmentalist and radical transgender activists, anti-police fanatics and other fringes. They have to be scrupulously specific about what, exactly, is "weird" about Maga Republicans to avoid a boomerang effect.

But the Minnesota Governor wasn't selected for stumbling upon this bon mot. Ms Harris is calculating he can help her launch a lightning-strike appeal to a huge swath of "middle America" where Democrats once held sway by appealing to middle class economic interests and appearing to champion "the little guy”. This may prove impossible, but it’s a commendably bold and gutsy strategy.

Ms Harris is, like Mr Trump, appealing to her base with her vice presidential selection, deciding to try to maintain her striking momentum – in some national polls she suddenly holds a slight lead over Mr Trump – by presenting an apparently all-progressive ticket. Yet both Ms Harris and Mr Walz will surely continue to tack to the political centre despite their strong liberal credentials.

At the black journalists convention, Mr Trump was asked if Mr Vance would be "ready on day one". Rather than affirming this, as any normal presidential candidate would about his running mate, Mr Trump simply averred that vice presidential candidates don't matter. Apparently he couldn’t bear admitting that anyone else, even his running mate, is a plausible president.

Apart from the appalling slight to Mr Vance, no doubt a small foretaste of the callous disrespect he can expect to come, Mr Trump wasn’t entirely wrong: most Americans vote for the top of the ticket.

The past six weeks have, at a dizzying pace, reshaped American politics as Ms Harris displayed unexpected poise, charisma and mass appeal. She’s gambling Mr Walz can hold the party together and speak in their own language to a large segment of the American people that the Bay Area prosecutor, Ms Harris, can't. That’s arguably a long shot given his staunchly liberal record, but it could be a winning formula.

Still, Ms Harris has all the momentum, with just three months to go. Mr Trump appears justified in his evident panic.