Market meltdowns have been a big worry lately, and for good reason. With President Trump imposing the highest tariffs since the Great Depression and enacting myriad other disruptive policies, the threat of another market crash can’t be ignored.

Yet despite an 18.9 percent downturn in the S&P 500 earlier this year, the stock market has rebounded. It has continually shrugged off shocks that, in previous years, may have set off a prolonged bear market.

In fact, stocks have become expensive again. While the potential for a serious market downturn hasn’t vanished, I think it’s also time to begin thinking about another problem: the danger of a market melt-up.

By many measures, we’re already in perilously overvalued territory. On a historical basis, share prices are high in relation to corporate earnings, assets and the size of the overall economy.

I don’t want to go too far with this. The U.S. stock market isn’t nearly as expensive as it was at the height of the dot-com bubble in the late 1990s and early 2000. But it is increasingly pricey — surprisingly so, when you consider the repeated blows to market sentiment dealt by the Trump administration.

Tariffs re-emerged as a major issue over the past week. The administration issued an array of announcements: Tariffs will increase, be delayed, not be delayed, be imposed on copper, be negotiated lower, be made permanent, and on and on. Who really knows? The stock market has been absorbing this information, stumbling from time to time but then regaining its footing. While the economic impact of the tariffs has barely been felt yet, the stock market remains much higher than it was at the beginning of the year.