For the past week, the Vikings have been making a bold proclamation: We are one player away.

The original announcement came by way of Air Wilf, the private jet that transported one of the NFL's top players to the Twin Cities last Thursday. Upon arrival, the Vikings spent 48 hours showcasing the franchise to the player and his girlfriend.

Tuesday night, the Vikings finalized an agreement to acquire that player, doling out the largest contract in team history along with three high draft choices.

Generally speaking, such a commitment is reserved for a team that otherwise considers itself ready to challenge for a championship.

It is also the kind of value normally placed on a quarterback, the single most critical position in professional sports.

Jared Allen, of course, is no quarterback. True, he plays the critical defensive end position. And yes, finding a star defensive end might be more difficult than getting an elite quarterback.

But even though the Vikings gave up a first-round draft pick and two third-round selections to the Kansas City Chiefs -- while also agreeing to give Allen a $74 million contract that includes more than $31 million guaranteed -- it is unfair and unrealistic to consider him that one player who can lift them to a championship. That job description will always fall on the quarterback's shoulders -- in this case, on Tarvaris Jackson's.

So in reality, here is what the Vikings were thinking Tuesday night: Tarvaris Jackson will be good enough in 2008 that we feel comfortable making an enormous investment toward winning the Super Bowl right now.

This thought is not exactly groundbreaking. Two credible NFL observers expressed similar hesitation earlier Tuesday, before the trade was finalized.

"That division is up for grabs," said former San Francisco and Detroit coach Steve Mariucci, now an NFL Network analyst. "Without [Brett] Favre in Green Bay, anyone can win the division. The Vikings are putting a pretty darn good football team together. They need their quarterback to play well. If he's better than last year, which he should be, they have a chance to win that division. Jared would be another piece of the puzzle."

Meanwhile, during an ESPN conference call, "Monday Night Football" analyst Ron Jaworski acknowledged Allen would be a "huge boost" for the Vikings defense and said they "are definitely going in the right direction."

Later, reporter Chris Mortensen asked Jaworski if he thought Jackson was ready to take the Vikings to the championship -- or if they should pass on the Allen trade and select a quarterback in the first round of the draft.

"[Jackson] is not there yet," Jaworski said. "He has a ways to go. But I think if you take a step back and go with a young quarterback, now you're looking at a further development at the quarterback position."

This is neither a diminution of Allen's expected impact nor a gratuitous shot at Jackson. It's a simply a reality check, a reminder that there is only one transcendent position in football. And it's not defensive end.

To be sure, the Vikings undoubtedly have built a strong team around Jackson. Allen's arrival gives the Vikings a potentially elite defense, one that we know can stop the run and now should be significantly more effective against the pass.

On offense, the Vikings have given Jackson an accomplished receiver in Bernard Berrian to stretch the field. Versatile fullback Thomas Tapeh will block for the NFL's most explosive running back in Adrian Peterson, and the offensive line returns all five starters for the first time since 2004.

Jackson has been hard at work all offseason, working on his decision-making and learning to avoid turnovers. After his second-half improvement last season (82.9 rating, accounting for nine touchdowns over the final seven games), it's reasonable to count on additional progress in 2008.

Will it be enough to put his team on a short list of Super Bowl contenders? The Vikings think so. Otherwise, they wouldn't have mortgaged their future, and their bank account, on their most expensive player acquisition since the Herschel Walker trade in 1989.

Allen is the type of player who can help turn a good team into a great one. But make no mistake: If the Vikings win the Super Bowl any time soon, that one player must be Jackson.

Staff Writer Judd Zulgad contributed to this report. Kevin Seifert • kseifert@startribune.com.