"What Next for the US Stock Market?"

Not "next" as in tomorrow but next as in the next major trend.
It's pretty easy, most folks can see it out there on the horizon. the bend at the end of the current trend, friend.
(sorry, old line, repurposed)

The trick is getting the timing right, or at least right enough for Q3 and Q4 to nail down some bonus money.

Here's Martin Feldstein, currently at Harvard and President Emeritus of the National Bureau of Economic Research. In a prior life he was chairman of the Council of Economic Advisers and picked up a John Bates Clark Medal.

From Project Syndicate, August 28:

August 22 marked the longest period of rising share prices in US history. But the stock market's nine-year bull run won't last much longer, as three factors drive up long-term interest rates, reducing the present value of future corporate profits and providing investors with an alternative to equities.

CAMBRIDGE – The US stock market achieved its longest rise in its history on August 22, with the Standard and Poor’s 500 index up by 230% since 2009. Although this wasn’t the biggest increase in a bull market, it marked the longest period of increasing share prices.

Several forces contributed to this impressive nine-year run. The primary driver has been the extremely low interest rates maintained by the Federal Reserve. The Fed cut its short-term federal funds rate to near-zero in 2008 and did not begin to increase it above 1% until 2017. Even now, the federal funds rate is lower than the annual inflation rate. The Fed also promised to keep the short rate low for a long period of time, causing long-term rates to remain low as well. With interest rates so low for so long, investors seeking higher returns bought shares, driving up their prices.

A rational model of share prices sets them equal to the present value of future profits. Low interest rates raised the present value of future profits, and the corporate tax reform enacted at the end of 2017, together with deregulation in several industries, has raised both current profits and expected future profits, contributing to the present value of future profits.

But even with rising profits, low interest rates have caused share prices to increase faster than profits. As a result, the S&P price-earnings ratio is now more than 50% higher than its historic average.

With real (inflation-adjusted) GDP rising at more than 3% this year, the strength of the US economy has induced foreign investors to shift their holdings to US equities. And in recent months, US households that had not owned stocks in the past, fearful of missing out on the bull market, have joined the equity bandwagon.

But what of the future? Stock-market booms don’t die of old age; they are generally killed by higher interest rates. That often happens when the Fed raises the short-term interest rate to stop or reverse rising inflation. Although the Fed’s preferred rate of inflation – the price of consumer expenditures – has just reached its target of 2%, other measures of price growth are rising more rapidly. The overall Consumer Price Index (CPI) is now 2.9% higher than it was a year ago. Even “core” consumer inflation, which strips out more volatile food and energy prices, has increased by 2.4% over the past year.

The Fed’s short-term interest rate is now just 1.75%, implying that the real rate is still negative. The Fed’s Open Market Committee has now projected that it will raise the federal funds rate to 2.4% by the end of 2018, to 3.1% by the end of 2019, and to 3.4% by the end of 2020.

My judgment is that the greatest risk to the stock market is the future increase in long-term interest rates. The interest rate on ten-year Treasury bonds is now about 2.9%, implying a zero real rate when compared to the current level of the CPI. Historically, the real ten-year Treasury rate has been about 2%, implying that the ten-year rate might rise to 5%.

Three factors will contribute to the rise in the long-term rate. The Fed’s projected increase in the federal funds rate will put upward pressure on the ten-year interest rate. With the unemployment rate at 3.9% and likely to decline further in the year ahead, the rate of inflation should continue to increase. And even if that does not cause the Fed to raise the federal funds rate at a faster pace, higher inflation by itself will cause investors to demand higher long-term rates to compensate for the loss of their funds’ real value....MORE

The 10-year at 5% would definitely curb enthusiasm for equities and much else.
We aren't there yet, and until markets have their collective Wile E. Coyote moment calling the top in equities is a tough thing to do.

And for what it's worth, that slightly negative real short rate is the only thing supporting gold.