Markets were mostly marginally higher on Tuesday.
Earlier on Tuesday, Asian stocks were mixed, the Nikkei closing flat and the Shanghai Composite Index falling 0.3 percent.
Peter Cardillo, chief market economist at First Standard Financial, said that the "market is on momentum roll" while noting that it has "just slowed down".
That slowdown could make this week critical for stocks next year.
Ari Wald, technical analyst at Oppenheimer, said that following a rally around the year-end, the S&P has gained on average 2.8 percent in the following three-month period.
However, if the market is down during the year-end, the S&P has averaged a 1.2 percent loss in the following three months.
But for now, Wald sees a continuation of the rally. "There's no sign of a meaningful top in place," he said.