Markets tumbled again on Monday after President Donald Trump said he wont rule out an upcoming U.S. recession, sending skittish investors into another sell off fueled by whiplash over tariffs, and overall economic uncertainty.When asked, Trump told Fox News on Sunday: I hate to predict things like that There is a period of transition, because what were doing is very big. Were bringing wealth back to America.Later, when pressed further, Trump said, All I know is this: Were going to take in hundreds of millions of dollars in tariffs, and were going to become so rich youre not going to know where to spend all that money.And so, this week starts off, as it ended, with market turmoil and even more tariffs. While across-the-board tariffs on good from Canada and Mexico are delayed, 25% tariffs on all steel and aluminum imports into the U.S. go in effect on Wednesday, aimed at China, but will effect Canada, Brazil and Mexico, where we get most of our steel. And many countries are promising to clap back with reciprocal tariffs, all of which will likely get passed on to American consumers.A look at the numbers shows all three major indexes fell in morning trading with the Dow Jones Industrial Averagedown almost 1%, S&P 500 shedding 1.7%, and the Nasdaq almost 3%. Both the S&P 500 and Nasdaq dropped to their lowest levels since September 2024, according to CNBC.Some of the biggest movers were tech stocks with Elon Musks Teslashares plunging down 8%, Palantir falling 7.5%, chipmakerNvidia shares falling 5%, and Meta and Alphabet both losing 4%, at the time of this writing. Not a pretty sight.Adding insult to injury, HSBC downgraded U.S. equities, saying there are better opportunities elsewhere, turning its eye toward stocks in Europe, citing the ongoing tariff debacle. What is a recession?Its unclear if we are heading into a recession, but what is clear, is how to measure one. A recession is defined as two consecutive (one after the other) negative quarters of gross domestic productthe value of all the goods and services the U.S. produces. But it can also be measured more broadly as a significant decline in economic activity spread across the economy, lasting more than a few months, normally visible in production, according the National Bureau of Economic Research (NBER)s Business Cycle Dating Committee, which tracks recessions. It looks at factors like unemployment, industrial production, real income, personal consumption, and wholesale-retail sales to determine the depth and breadth of economic decline.So far, the NBER has not declared a current recession in the U.S.Will there be a recession?Some experts say they are more worried about inflation, than a recession, and that while Americans worry about tariffs, that isnt a great indicator of upcoming consumer spending. (Inflation measures how much prices are going up, while a recession measures a period of time where there is negative economic growth, according to Fidelity Investments.)Demand is showing some fraying around the edges, but it hasnt accumulated to enough to be a meaningful risk of a downturn, Vincent Reinhart, chief economist at BNY Investments told CNN. Inflation is still a top priority.The Federal Reserve seems to also be more worried about inflation. Based on what we know today, given all the uncertainties around that, I do factor in some effects of tariffs now on inflation, on prices, because I think we will see some of those effects later this year, New York Fed President John Williams said, as reported by CNN. Going forward, the big question will be if inflation worries gain enough steam so we could see another rate cut. Well have to wait and see. Meanwhile, Holger Schmieding, chief economist at Berenberg Bank, told CNBC on Monday, I dont think we will talk about a U.S. recession. The U.S economy is resilient, I would say, largely despite Donald Trump but was quick to call Trump an agent of chaos and confusion.