Image source: Priceline.  

There's no denying that The Priceline Group (NASDAQ:BKNG) is the market darling among the leading travel portals. The parent company of, Kayak,, and even the OpenTable restaurant reservations site has seen its stock roughly triple over the past five years.

It's had a rough start to 2016 -- like most stocks -- but will it bounce back? Priceline's had its ups and downs on the course to its overall ascent, so let's go over some of the things that could lead to a bumpy flight for investors in the near term. 

1. Travel itself can fall out of favor
Growth for the online travel space a decade ago consisted largely of swiping bookings from traditional travel agencies. The migration has already happened, and that means that Priceline's success is riding on the whims of the travel industry itself. It's no longer a matter of grabbing a bigger slice of the pie. Online travel is the pie.

We're traveling at a healthy clip these days, but terrorism and an economic downturn could change that. Obviously these are the same factors that could sink most stocks, but online travel is susceptible if conditions make it less compelling to travel for pleasure or business.

2. A strengthening dollar can sting results
The dollar's been gaining ground on global currencies, and that's an issue at Priceline. You might be surprised to learn that just 12% of the gross bookings at Priceline in its latest quarter -- $1.7 billion of the $14.8 billion total -- were U.S. bookings. 

Priceline's is a beast in Europe, and with the U.S. dollar gaining against European currencies, it's starting to eat into top-line results when they get translated back for stateside reporting. Priceline's latest quarter saw gross bookings rise 7% on a reported basis since the prior year, but it was a heartier 22% on a currency neutral basis.

That's not the only way that weak European currencies can hurt. can feel the pain if it keeps Europeans from traveling internationally to countries where currencies are strengthening. This is important since U.S. gross bookings have actually declined for Priceline over the past year, putting more weight on Priceline's international operations.

3. Needle-moving acquisitions could become scarce
A big reason for Priceline's market-thumping success is its ability to make timely acquisitions and investments in potential disruptive sites. When comparison shopping site Kayak threatened to make traditional portals obsolete by searching across several options at once, Priceline snapped it up. As OpenTable gained traction as the online reservations platform of choice for top restaurants, Priceline picked it up as a way to reach deeper into the travel experience. 

Just last month Priceline expanded its investment with Ctrip (NASDAQ:CTRP). Priceline and an investment firm teamed up to invest $500 million in Ctrip's convertible bonds. The agreement allows Priceline to hold as much as 15% of Ctrip's outstanding stock, giving it a foot in the door in the promising Chinese market.  

What's left? Disruptors will continue to come, but they may be search engines and social sites that are too big for it acquire. Priceline also can't snap up the actual travel providers if they get better about marketing directly to consumers. Organic growth will be a bigger part of its future, and that could be a problem for investors during an operating lull.