With young, talented cores, the Blackhawks and Penguins remain solid Cup contenders this season. (Getty Images)

By Allan Muir

It's a funny thing about windows. Sometimes you can't tell if they're open or not until you pass through . . . or run smack into them.

That's usually the way it plays out as teams work to establish themselves as legitimate challengers for the Stanley Cup. Those years spent carefully assembling the pieces require more than vision. They hinge on perfect timing. Because just when everything seems to be place, injuries can deplete the depth or the scoring dries up or the chemistry experiment fizzles. It doesn't take much to derail the dream.

Every team aspires to contention, but few teams are ever actually in the sweet spot where everything comes together and puts them directly in the hunt. The defending champion Blackhawks are there now. So are the Bruins and the Kings, and perennial contenders like the Red Wings and Penguins, too.

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And then there are the teams for which opportunity is either just over the horizon . . . or just slipping from their grasp. For them, the window of opportunity is slowly opening or closing right in front of their eyes.

Here's a look at three clubs that are rounding into Cup-contending form this season, and three that may have passed their best-by date.

Opening

Playoff disappointment has been part of the learning curve for the Blues. (Jeff Vinnick/Getty Images)

St. Louis Blues

If last season's thrilling seven-game loss to the Kings suggested anything, it's that the Blues could really use a cold-blooded sniper capable of breaking a game open at any moment. But the absence of that player doesn't mean they're still stuck in the second tier of hopefuls. In fact, like recent champions Los Angeles and Boston, the Blues are a team whose success will depend on layer upon layer of depth and experience. That's the element they chose to strengthen over the summer, adding Derek Roy, Maxim Lapierre, Magnus Paajarvi and Brenden Morrow to a forward corps that was already capable of playing it any way you wanted. They may have found another intriguing piece for one of the league's deepest bluelines in Ryan Whitney. And while they lack that elite goalie, they have three options in Jaroslav Halak, Jake Allen and Brian Elliott who have shown they can get hot and carry the team for long stretches. With a proven winner in Ken Hitchcock calling the shots, St. Louis is ready to take that next step.

Washington Capitals

The Caps have kidded themselves about their status as contenders throughout the Alex Ovechkin era, believing their nuclear arsenal more than made up for a lack of homeland defense. Six disappointing springs later, they might finally have figured out how to launch a legitimate challenge.

It all starts with Ovechkin, of course. After adapting to a new position, the defending Hart Trophy winner played some of the most effective and consistent hockey of his career. But he's just part of a forward corps that's deeper, and better balanced, than in the past, with players like Martin Erat, Mikhail Grabovski and Tom Wilson ready to fill glaring needs. Karl Alzner has matured into a reliable shutdown defender, while John Carlson and Mike Green provide plenty of flash from the back end (although they desperately need an upgrade over John Erskine in the four spot). And while Braden Holtby fell apart against the Rangers in Game 7 of their first round series last spring, his body of work in the playoffs, along with his invite to Team Canada's camp, speaks directly to his potential. With Adam Oates at the helm, the Caps are a team finally ready to live up to their own hype.

Ottawa Senators

The surest sign that the Senators are on the right path is the recognition that they won't catch anybody by surprise this time around. Last season played out like a feel-good movie. They were a projected cellar dweller struck by a litany of injuries that should have left them battling the Avalanche for the top spot in the draft. But instead of folding, the Sens banded together under Adams Award-winning coach Paul MacLean to earn a playoff spot, relying on the sort of all-hands-on-deck mentality that will serve them well as they learn to play as contenders.

The loss of captain Daniel Alfredsson to Detroit will be felt more by the fans than the team, which should end up being stronger up front with the addition of steady sniper Bobby Ryan and the maturing of promising youngsters like J-G Pageau and Mika Zibanejad. And with a back end led by a healthy Erik Karlsson and all-world stopper Craig Anderson, they'll hold the fort as well as anyone.

There's always the chance that the Sens will fail to match last season's success, or maybe even take a step back. That happens sometimes to teams on their way. But it'll be just a bump in the road, a temporary setback. Ottawa is on the verge of something big.

Closing

Steely new coach John Tortorella while try to flog the withering Canucks on another Cup run, (Bob Frid/Icon SMI)

Vancouver Canucks

Hard to believe that a team that was one home win away from skating the Cup just two years ago has been reduced almost to the point of irrelevance. Sure, the Canucks have the talent -- especially on the blueline -- to win plenty during the regular season. But come playoff time, they're skeet. They're too easy to push around, core star Ryan Kesler can't stay healthy, and they have a goaltender who literally doesn't want to be there. Even if the Sedins agree to new deals (as most expect them to), they're simply signing on to run out the clock. The best days have passed for this core group.

San Jose Sharks

There are two ways San Jose GM Doug Wilson can play the hand he's dealt himself. Either go young, with recently extended forwards Logan Couture and Joe Pavelski as his team's centerpieces, or double down on aging vets Joe Thornton, Patrick Marleau and Dan Boyle in the hope that they'll finally put together that long-awaited Cup run in the couple of good years they've got left. That one might seem to be the path of least resistance -- after all, there's still tread on their tires and the fans love 'em. But considering how they've underperformed as a group in the playoffs, and how their goals-per-game average has decreased in each of the past four seasons, there's no reason to think they'll suddenly pull it all together. These Sharks have talent, but its a lousy mix -- like lobster stuffed with taco fixings. The smart play would be to move on from the expiring contracts, but Wilson won't do that. And that's why this team's Cup dreams have withered on the vine.

New York Rangers

Could this season be the last, best chance for these Rangers? It all depends on the team's pivotal player, Henrik Lundqvist, and his willingness to re-sign with the Blueshirts once his current deal expires next summer. While it seems unimaginable that he'd go elsewhere, Ottawa fans can tell you the story doesn't always end the way you expect.

With King Henrik in net, anything is possible for New York, a team blessed with a capable blueline and a forward corps that's better positioned to reach its potential under new coach Alain Vigneault. But if Lundqvist -- who is either a master at playing it cool or truly is ambivalent about signing a new deal -- goes in another direction, the Rangers are in trouble. The system is devoid of an obvious successor (Jeff Malcolm, a free agent signing out of Yale this summer, is the best bet and he's not close) and the market options (Ryan Miller, perhaps?) take the team a step back. This is a pivotal year for the New York.