Hello and welcome to the Intelligence on Economist Radio. I'm your host, Jason Palmer.

Every weekday we provide a fresh perspective on the events shaping your world.

Since 1986, the Economist's annual Big Mac Index has proved a beefy measure of which of

the world's currencies are overvalued or undervalued. We run through this year's list

to find out where to go if you want to do some burger-based arbitrage.

And India has two local environmental problems, piles of pine needles that represent a fire

risk in the Himalayan foothills and rivers polluted by heavy metals. Now a team of scientists

has figured out how to turn one into a solution for the other.

Let's start, though.

Every night, since the end of May, thousands of Americans have taken to the streets of their

cities to protest against systemic racism and police brutality.

The demonstrations have been particularly loud in Portland, Oregon, a left-leaning city

in America's northwest. And they've become even louder in recent weeks, as President

Donald Trump, whose campaigning for re-election on a law and order platform, sent more than

a hundred federal law enforcement officers into the city. In doing so, he's pitted himself

not only against the protesters, but also against Portland's mayor and district attorney,

who have called the intervention on lawful. And with Mr. Trump threatening to expand this

use of federal forces into other American cities, the fight may only be beginning.

On June 26, Donald Trump signed an executive order authorizing the dispatch of what he

called personnel, but which actually mean federal law enforcement officers, to cities

to protect federal property and monuments.

John Fasman is the economist Washington correspondent.

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