The stock market's ascent to new highs has created new hopes of further gains in President Donald Trump's inaugural year.

But in light of one important statistic, a sustained bull run in the stock market under the Trump administration is becoming less likely, according to the Wall Street Journal. When speaking of market valuations, analysts and strategists normally focus on price-earnings (P/E) ratios. A less commonly used statistic is the ratio of the total value of the stock market to gross domestic product (GDP), and we’re rapidly approaching a 17-year high on that basis, the Journal says.

The total value of U.S. stocks ended 2016 at about 169% of GDP, according to the Journal. The previous high was 177% at the end of 1999. Bearish investors will note that this lofty valuation resulted from speculation in the new Internet economy, which produced the so-called dotcom bubble. The ensuing dotcom crash lasted two and a half years and knocked 78% off the value of the Nasdaq Composite Index. (See: Market Crashes: The Dotcom Crash.)

The Market Under Obama

The S&P 500 rose by 166% under President Barack Obama, the Journal reports. During his term of office, the forward P/E ratio on the S&P 500 rose from 11 to 17. Additionally, corporate profits surged, partly through shifting work to lower-cost locations abroad. Trump’s protectionist agenda is likely to make it harder for companies to move production abroad. As a result, earnings gains from similar kinds of labor cost reductions will be more difficult to achieve in the future, the Journal observes in its January 22 story.

By contrast, Obama took office on January 20, 2009 near the market's recent bottom in the wake of the financial crisis, which had produced a major market crash. At the end of 2008, the ratio of the S&P 500 to GDP was 85%, just over half what it is now, according to the Journal. (See: Trump Will Get the Market’s 100-Day Report Card.) Through critics say Obama failed to do enough, his stimulus package and rescue plans for the banks and automakers set the stage for sustained growth in the economy and stock market.

Trump's Opportunity

Many of Trump's policies have the potential to add to earnings and economic growth if they're fully executed, including $1 trillion in infrastructure spending, massive corporate tax cuts and deregulation of the financial services industry. But assuming that the market is already pricing in an optimistic scenario for profits under Trump's policies, a significant increase in economic growth may be necessary for further earnings expansion and market gains, the Journal states. Trump’s economic team is forecasting annual GDP growth in the range of 3-4%, a goal that will require a robust combination of workforce expansion and productivity gains that are theoretically possible, though a stretch given current conditions. (See: Depression-Era Headwinds Restrain the Economy.)

The bulls, of course, argue there's room to move upward. While the forward P/E ratio on the S&P 500 is now in a historically expensive range, at around 17, that's well below the stratospheric level of 28 that it reached during the dotcom bubble, the Journal observes.