It’s not China’s Xi Jinping, although as head of the world’s secondary superpower, he’s certainly catching up.

Nor is it the EU, IMF or the Pope. It’s something quieter, more calculating – and far less forgiving.

Even Donald Trump has retreated when faced with its power. At least for now.

Trump has taken the power of the US presidency to new levels.

Not just because the US remains the world’s largest military and economic force, but because his ego demands domination.

He plays the stock market like a one-man band – pumping it up with boasts, crashing it with threats, then pretending it was all part of the plan.

Trump wiped trillions from global pension funds with his global trade tariffs on April 2 – what he laughably dubbed “Liberation Day”.

Then on Wednesday, he sent stocks skyrocketing with news of a 90-day pause. This triggered one of the largest "relief rallies" in US history.

It was a dramatic turn worthy of reality TV. Which is what Trump understands best.

But behind the bravado, he's exposed the limits of his power by confirming that there is a greater authority out there.

Trump has finally met his match. It’s called the bond market.

Governments issue bonds to fund spending, which are bought by big pension companies and other institutions.

If bond investors lose faith in the government that's issuing them, they either demand more interest or go on strike and refuse to buy.

They're known as the "bond vigilantes", as they punish leaders who step out of line.

Former Tory PM Liz Truss discovered that the hard way, following her disastrous mini-Budget in September 2022.

Unimpressed bond investors demanded eye-watering interest rates to lend to the UK, sending mortgages soaring and pensions into a death spiral.

Truss was gone faster than you could say wet lettuce. That’s the power of the bond market.

Labour Chancellor Rachel Reeves lives in fear of the bond vigilantes. They'll burn her house down unless she bucks up.

Reeves knows its power, and the limitations of her own.

Back in the 1990s, Bill Clinton’s campaign strategist James Carville famously said: “I used to think if there was reincarnation, I wanted to come back as the president or the pope… but now I’d like to come back as the bond market. You can intimidate everybody.”

As we discovered on Wednesday, that includes Trump.

The bond market doesn’t shout or rage or tweet or hold press conferences. But when it moves, governments fall.

US Treasury Secretary Scott Bessent personally warned Trump that he was on the brink of igniting a full-blown financial crisis. And for once, Trump backed off.

But only a bit.

He’s still left a blanket 10% charge on all imports, a 25% penalty on cars, steel and aluminium, and a massive 145% hit on goods from China.

His so-called pause was a tactical retreat, not a strategic rethink.

The Donald can’t stand the idea of anyone – or anything – having more power than he does. And certainly not a silent, faceless financial force.

This battle isn’t over. Trump will come back for more.

Who will ultimately win? History suggests it will be the bond market. As the battle rages, our pensions and Stocks and Shares ISAs will be caught in the crossfire.