Kevin Hassett, a senior economic advisor to President Trump, told CNBC's Squawk Box Monday that the U.S. is likely to experience a GDP decline of between 20% and 30% in the second quarter.

Why it matters: Hassett said the decline, driven by the coronavirus pandemic, will be the "worst since the Great Depression."

What he's saying: "The really bad news we've been seeing in the initial [unemployment] claims will be spread out over a couple of months, but I'm expecting that when we see the unemployment for the first week of May, we're gonna see a number that's maybe 16%, 17%."

"The question is 'What happens next?' And that's what we're focused on right now in the White House."

The big picture: Around 26.5 million American workers have filed for unemployment benefits in the past five weeks, and unemployment is likely already at Great Depression-era highs.

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