By Izin Akhabau

Listen to this briefing

Good morning. It’s Monday, Aug. 24, and I can’t stop looking at this rare blue tree frog that was spotted in a Virginia park. Now, let’s get to the news.

	The U.S. and Canada are locked in a trade fight.

• In a shocking move: Canadian leader Mark Carney quit trade talks rather than accept concessions. In response, the U.S. imposed 50 percent tariffs — and Canada promised to retaliate.

• It could be bad news for your pocketbook: Former vice president Mike Pence said the trade war poses new risks for the economy. Americans are already struggling with high costs.

• Zooming out: President Donald Trump’s aggressive trade strategy may be reaching its limits — read our analysis here.

	A legal argument for the White House ballroom may have a serious flaw.

• According to Trump: The White House needs the ballroom for national security reasons. An emerging legal argument says it would provide future presidents with a secure, hardened facility.

• However: Former officials say that argument fails to acknowledge the underground bunker that was secretly built after 9/11. It’s nuclear-proof and could house the president and aides for weeks.

Doctors say Trump’s weight poses a significant health risk.

• What to know: The president seems to have gained about 20 pounds since his last campaign. As of May, Trump’s weight puts him just 1.6 pounds shy of being classified as obese.

• Yesterday: About 150,000 spectators attended the first IndyCar street race in D.C. — Trump’s Freedom 250 Grand Prix. The president waved a green flag to start the competition.

A leaked memo shows how the U.S. is lobbying against global plastic limits.

• The details: The memo says restricting plastics and chemicals could limit access to weapons materials. It comes amid four years of global treaty talks on plastic limits.

• The bigger picture: Global plastic pollution has hit over 57 million tons per year. Dozens of countries say the problem will become overwhelming if restrictions aren’t imposed.

Fighting measles comes at a high cost to taxpayers.

• A huge effort: Measles is the most contagious vaccine-preventable disease, and moving quickly is essential to containing its spread. See how much it costs to contain just 10 cases here.

• More in health: New vaccines for melanoma could revolutionize cancer treatment. 73-year-old Mark Orwig, who had melanoma, was part of the clinical trial and told The Post all about it.

An invisible force is driving destructive floods across the U.S.

• What is it? Water vapor. A record-breaking El Niño, marine heat wave and ocean warming from climate change in the Pacific have sent more moisture than usual into the atmosphere.

• The danger: Though moisture levels don’t directly increase rainfall amounts, they can boost the odds of extremes. Flood risks may intensify in these states during fall and winter.

Readers had notes on The Post’s list of the most influential works of American culture.

• This year: Our critics, reporters and editors spent months creating, revising and arguing over the defining acts of U.S. culture. We settled on a list of 25 works published last month.

• It proved controversial: We received hundreds of messages after asking for feedback from readers, who pointed out some big omissions. See what they thought was overlooked here.

Before you go ... don’t ignore abdominal pain: