Tonight on PBS News Weekend, Volodemar Zelensky goes to London to rally European support after the fiery exchange in the Oval Office signals are rift in U.S.-Ukrainian relations.

Then Canada braces for a trade war after trying to head off the steep tariffs

Washington is set to impose next week. And why medical experts say the risk of dementia for people

over 55 is much greater than previously known.

If you're thinking about your lifelong health, it makes you realize that you need to consider

the risk that at some point, you may hit dementia before death. Good evening. I'm John Yang. Tonight, Washington and European capitals are still feeling the

reverberations of yesterday's heated Oval Office exchange between President Trump and Ukrainian

President Volodemar Zelensky. Hours after Mr. Trump scolded Zelensky for not showing enough appreciation for U.S. support,

the Ukrainian leader posted on X,

we are very grateful to the United States for all the support.

I'm thankful to President Trump, Congress for their bipartisan support, and the American people.

He also reiterated his opposition to a quick ceasefire

that President Trump wants, saying Russian leader Vladimir Putin can't be trusted. Now Zelensky

is in London to rally the support of European leaders. Today he met with UK Prime Minister

Kier Sturmer, and tomorrow he'll attend a European summit in London to discuss the way forward.

Kurt Volker is a former U.S. Special Envoy to Ukraine and a former U.S. ambassador to NATO.

Mr. Volker, what do you expect to come out of this European summit tomorrow that Zelensky is attending?

Well, I think there are some good things that we've seen already, these expressions of European

support and solidarity for Ukraine.

I think it's important for Zelensky psychologically.

I think it's also important for the Ukrainian people.

But I hope that behind closed doors, they're actually talking about what kind of things

...