Wharton School finance professor Jeremy Siegel appears to be wandering from the bull camp.

Siegel, who helped lead 2017's rally cry, told CNBC's "Trading Nation" that he isn't blaming Italy's political turmoil, the latest headline to rock the markets, for a borderline bearish forecast.

Rather, he cited risks from rising rates to trade tensions.

"The major threat of the market is higher interest rates going forward. Too many people read the FOMC minutes as being too dovish," he said Wednesday.

Siegel expects the Federal Reserve to hike rates a total of four times this year, a number Wall Street may be dangerously underestimating. As rates rise, stocks historically look less appealing to investors.

He's also viewing trade tensions with China as a "wild card" for the market.

"[President Donald Trump] feels he has to tread very, very carefully on this. It doesn't mean for sure he won't go full blast forward," Siegel said. "Caution is going to be the word here."

His thoughts came as stocks staged a comeback a day after Italy tensions rattled the market.

The Dow grabbed 306 points to close at 24,667. But it still fell short of breaking even from Tuesday's losses.

Siegel has been warning since December that 2018 wouldn't be as robust as 2017, and stocks would be flat to up 10 percent by year-end.

"This is a great year for earnings, no one argues with that. But the tax cut is front-loaded which means that the write-offs on capital equipment are going to accrue to 2018 and not nearly as much in 2019," Siegel said.