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Consumer spending has powered the US economy to nearly a full year of defying expectations.

But exactly who is doing that spending is changing. And opening up a new question about the next phase of this economic expansion.

A new report from economists Morgan Stanley published late last month showed the top quintile of earners — or households in the top 20% of income — has accounted for 45% of all consumer spending between 2020 and 2022. Since 2004, this cohort has typically accounted for closer to 39% of all spending.

So the question now is what would would make this wealthy cohort slow or stop spending.

On this front, Morgan Stanley's team has some ideas.

Historically, rich people have slowed spending when their financial assets lose value, i.e. stock prices drop like after the tech bubble, or real estate values fall like during the 2008 financial crisis.

As readers are well aware, stock and home prices have risen sharply since 2019, though Morgan Stanley expects the latter to stall out next year.

"Our outlook calls for high-income consumption to slow as the boom years of the post-Covid services recovery moves further into the rear view mirror," wrote the firm's economist Sarah Wolfe.

"And indeed our analysts who cover restaurants and luxury brands both point to an aspirational (middle-income) consumer that has begun pull-back spending on fine dining and luxury shopping. As wealthy households approach satiety as well, aggregate consumer spending will shift into a lower gear. For a sharper step-down, broad-based white-collar layoffs and [a] significant loss of wealth, particularly in housing, are key."

On the one hand, resilient consumer spending is a good thing. Just look at the first estimate of third quarter GDP released on Oct. 26 as an example.

This spending also supports demand for goods and services, contributing to the job market holding up and serving as the main reason the economy hasn't (yet) fallen into recession.

On the other hand, this robust spending is one of the factors contributing to the persistence of inflation, which hurts lower-income households more.

As McDonald's (MCD) CEO Chris Kempczinski pointed out on his company's earnings conference call this week, "One of the things that we saw industry-wide is that that low-income consumer, which we would say is $45,000 and under, was negative from an industry standpoint."

So, wealthy consumers appear to be doing fine. Lower-income consumers are hurting. These are dynamics many investors already have a beat on.

But what has weighed on lower-income consumers won't be what brings down bigger spenders, or the economy at large.

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