Pros: Beware these big threats to rally

Biggest threat to market
Biggest threat to market   

Talk about a winning streak. The Dow Jones industrial average has marched higher for five consecutive sessions with bulls insisting that, if anything, tailwinds are growing stronger.

Buyers say better-than-expected earnings, as well as lower prices at the pump and relatively positive economic data provide three powerful catalysts that should drive a slow churn higher into the end of the year.


Trader on the floor of the New York Stock Exchange.
Getty Images
Trader on the floor of the New York Stock Exchange.

It would seem as if nothing can stop this market.

Jack Ablin of BMO, however, has a few concerns. First and foremost, he's worried current valuations in the market aren't sustainable. Ablin, like many other skeptics, says the premiums on stocks are so great, that even a relatively small negative could send the S&P 500 tumbling.

And he thinks Europe is anything but a small negative. "There's significant weakness abroad and it could easily filter into our market," he said.

Also, Ablin added a large portion of the recent rally involved a rotation from bonds into stocks as low interest rates forced investors to seek yield in the stock market. "We've been rallying on liquidity for the last six quarters," he said, "but I'm starting to see liquidity drying up," which suggests less money may be flowing into the market.

Read MoreUS companies now stashing $2 trillion overseas

David Lebovitz of JP Morgan Asset Management sees another problem for stocks. "We've got a strong dollar that's just getting stronger." When multinationals repatriate profits in other currencies, "it could have a very negative impact on earnings."