U.S. stocks had been on a tear in December, putting themselves in the position to post once-in-a-generation annual gains

In fact, the S&P 500 index SPX, +1.59% was having such a great run that as of Friday’s close, it looked likely to surpass 2013 performance, and notch its best calendar-year gains since 1997.

But with the index down 16 points, or 0.5% to around 3,223 as of midday Monday, it’s looking less likely that it will close above the 3,248.87 level by the end of the tomorrow, which it would need to beat 2013’s 29.6% advance and mark the large-cap index’s best calendar-year performance since 1997, when it gained 31%.

Options markets are pricing just 10.5% probability of closing above 3,250 tomorrow, according to JJ Kinahan, chief market strategist for TD Ameritrade AMTD, +1.80% , after hitting an intraday high of 3,247.93 on Friday, less than a point away from the milestone.

“The market continued strong into today,” Kinahan told MarketWatch, but said that Monday’s session “looks a bit more like profit taking as we see weakness in both equities and bonds.”

For context, 1997 was the year the movie “Titanic” debuted in the theaters and Elton John’s remake of “Candle in the Wind” — rewritten to commemorate Princess Diana after her death that August — was the best selling single of the year; music you couldn’t have streamed on Spotify SPOT, +2.04% or even downloaded on Napster, which was still about two years from invention.

It was also the year before the American polity was embroiled in its last impeachment saga, as the Monica Lewinsky scandal that catalyzed President Clinton’s impeachment wouldn’t become public until January of 1998.

And it was so long ago that it was even possible for a human to beat a computer in chess, though by May of 1997 IBM’s IBM, +0.72% Deep Blue supercomputer had proven its supremacy by beating then world-champion Garry Kasparov in a six-game match.

History gave reasons to believe the S&P 500 can eke out the gains it needs to surpass 2013, given the performance typically seen in stocks in the final week of the year. Since 1950, the S&P 500 index has gained an average of 1.3% in the final five days of the trading year and first two of the next, a phenomenon known as the Santa Claus rally.

This year, however, the market is down slightly from the market open on Dec. 24 through midday Monday.