NEW YORK (TheStreet) --With the S&P 500 in decline today, it sheds a light on the negative performances small-cap stocks have had recently. The Russell 2000 has fallen about 6% over the past month alone. Crossing Wall Street editor Eddy Elfenbein explained what he feels is causing the weakness during CNBC's "Power Lunch" on Tuesday afternoon.

"I think there's just some nervousness heading into the election. But remember, if we back up to really since most of this year, small caps have been doing quite well. In late August we saw over 400 stocks in the S&P 500 were above their 200-day moving average, that has gradually slid down," he explained.

As the slide has taken place leadership in the markets has become narrower and narrower, due to a shift in investors re-assessing risk, Elfenbein noted.

"I think traders are particularly concerned about the Fed meeting tomorrow and also the election coming up, that's what we're watching," he added.

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