Tariffs on Canada, threats against Iran’s partners and bond market intervention show a president weaponising US power while making Americans poorer at home

Three moves in the last week have exposed the limits of Donald Trump’s economic bullying. The US slapped 50% tariffs on another $20bn of Canadian goods – then threatened the same rate on the cars, trucks, parts and steel that America Inc depends on. On Monday, the Treasury secretary, Scott Bessent, menaced Iran’s trading partners with exclusion from the US financial network, hoping that coercion can deliver what months of war have not. And as the costs of war, tariffs and pro-billionaire tax cuts helped send US bond yields higher, the Treasury stepped in to tame long-term rates. These are not contradictory policies but a gamble: that US economic power can be repeatedly weaponised without reducing others’ willingness to depend on it.

The Trump administration’s “D-day” sanctions are potentially the most consequential because they expose the scaffolding of American financial power. While markets shrugged off the immediate threat, that calculation might change were the US to target a major Chinese refinery or bank. Such an escalation could spark a trade war with Beijing. The US has leverage. But China has pressure points – especially farmers in Republican states – that make using it costly. In the long run, there is a price to pay. Nations hold one another’s currencies partly because they trust the political relationship. Mr Trump is testing what happens when they don’t.

The president’s empty advice that children should receive separate jabs against measles, mumps and rubella will only lead to less take-up by parents

Nobody wants to hurt a child. The howl of pain, the tears, the look of betrayed shock all make it very hard to deliver a cherished small person to the needle-wielding nurse. But that’s part of being a responsible parent. It becomes a lot tougher if mum or dad is being fed mixed and erroneous messages about the benefits and harms of vaccination.

Parents have to make a lot of decisions about what’s right for their child, from the school they should go to and the food they should eat to the hours they should spend on the phone or watching TV. In the US, Donald Trump wants them to add another: do they choose to give their children separate jabs against measles, mumps and rubella, involving six visits to the clinic, or should they opt for the combined MMR vaccine, which does the job in two? For decades, the vast majority of families have been taking the advice of doctors, accepting their assurance that the MMR vaccine is safe and very effective. But what are they to think when a US president announces that the triple jab could be “quite lethal” and signs an executive order advising states to offer separate vaccines?

The Trump administration’s ‘America first’ approach has contributed to the scale of the crisis now unfolding in one of the world’s poorest countries

For months health experts have warned that the scale of the Ebola outbreak in the Democratic Republic of the Congo (DRC) could surpass the one that swept west Africa in 2014-16. This week, the authorities in the DRC announced that a grim milestone has already been passed: at least 2,325 people have died from the virus, making it the deadliest of the country’s 17 outbreaks and the fastest-growing in history.

There is no effective vaccine against Bundibugyo – a rare strain of the virus that spread fatally undetected during the spring, often being misdiagnosed as malaria or typhoid. In contrast to neighbouring Uganda, which succeeded in eliminating an outbreak, multiple factors are combining to let the disease rip through the DRC. The worst-affected region is contested by armed groups, and a context of population displacement and chronic insecurity has made monitoring and surveillance more difficult. Ebola treatment centres have been attacked as a result of misinformation and community distrust.