While the Standard & Poor's 500 Index (S&P 500) has rallied to several fresh records, both Treasuries and the U.S. dollar have failed to keep up, a development that one equity strategist has identified as cause for concern, according to CNBC. Matt Maley, a managing director at Miller Tabak, pointed to this disconnect, as well as the stock market's inflated values, to assert that stocks could encounter some headwinds early next year. (For more, see also: Overbought Stocks Vulnerable to Tax Reform Selloff.

The S&P 500 has climbed more than 18% year-to-date (YTD), according to Google Finance data through the close of trading on December 20. According to the relative strength index, a technical indicator, the benchmark group of stocks is highly overbought, CNBC reported. If the proposed federal tax bill receives approval, it could trigger a "sell the news" reaction. 

^SPX Chart

^SPX data by YCharts

While the S&P 500 has risen sharply this year, the iShares Barclays 20+ Yr Treasury Bond exchange-traded fund (TLT) has traded within a modest range for several months, according to data provided by YCharts. 

TLT Chart

TLT data by YCharts

The AMEX Dollar Index has also failed to follow the S&P 500 higher, moving within a relatively narrow range in the last several months, according to additional data provided by YCharts. 

^DXY Chart

^DXY data by YCharts

While the continued upward movement in stocks signals that the market expects tax reform to bolster the economy, the range-bound price movements of both U.S. Treasuries and the the U.S. dollar have offered conflicting signals, according to CNBC. 

Mid-Term Election Speed Bump?

Another factor that could hinder the stock market's upward climb is the mid-term elections that are scheduled to take place next year, according to a separate CNBC article. The S&P 500 usually declines during years that hold these elections, analyst Sam Stovall said during CNBC's Futures Now. He emphasized the general uncertainty surrounding this event. 

"Will the Republicans lose control in one or two houses? What will that do for infrastructure spending [and other policies]?" he asked during the show. (For more, see also: Stocks Will See 'Melt-Up' Into 2018 As Buyers Chase Profits.)