While Edward Yardeni, president of Yardeni Research, remains positive on stocks, he sees three possible roadblocks for the five-year-old bull market.

"The first is that price inflation makes a surprising comeback," he writes in his daily commentary. "I would certainly be surprised. So would the Fed."

There is a small chance that an increase in the federal funds rate in response to higher inflation would trigger a financial crisis, Yardeni notes.

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The second risk is a "melt-up" that pushes stock prices up too far, too fast. "The problem with melt-ups is that they tend to be followed by meltdowns," he explains.

"It's actually hard to relax in a melt-up, because the faster that stocks go vertical, the more we have to worry about picking the top and getting out."

Finally, there's a possibility of a geopolitical crisis, Yardeni says. It could be a spat between China and its neighbors or between Shiites and Sunni Muslims among other conflicts, he maintains.

"In the past, geopolitical crises that caused oil prices to spike tended to lead to recessions and bear markets."

But for now, Yardeni says he continues to "run with the bulls" for "the same old reasons." Those would be global central bank easing and strong earnings.

Stocks fell slightly Tuesday after the S&P 500 and Dow Jones Industrial Average hit record highs again Monday.

"It shouldn't be a shock to anyone that we're seeing softness after a blistering recovery," Chad Morganlander, a fund manager at Stifel Nicolaus, tells Bloomberg.

"This is a temporary reprieve from a market that's been seeing highs. By no measure does this mean we're going to get a bear market correction, but a 5 percent move down shouldn't come as a surprise."

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