Who has to step up?

I sarcastically made enough comments about the Ravens and Nationals making the postseason every year that I covered them that I might as well take responsibility for what happened last night, as well. The year that I stop covering the Ravens, they win a Super Bowl. Call it the Reverse Kolko Factor. Now that the NFL season is over, there's nothing but time standing between us and the start of baseball season. I fly down to Viera, Fla., in just six days, and the first official workout for Nationals pitchers and catchers is a week away. Before you know it, Grapefruit League games will be upon us. At this point, there are very few question marks surrounding this team as spring training approaches. Some squads might still have a hole in the rotation or a starting spot up for grabs in the outfield. Not this team. The eight starting position players are pretty much set, barring injury. Denard Span will sit atop the order and roam center field, Jayson Werth will be bumped down in the order and Adam LaRoche will return to provide pop and balance to the lineup. The rotation is complete, with Gio Gonzalez's off-the-field issues lingering as something that could throw a wrench into Mike Rizzo and Davey Johnson's pitching plans. The only issue the Nats have when it comes to starting pitching is what will happen if a starter is injured or Gonzalez is suspended for his involvement with Biogenesis, the Miami-area anti-aging clinic that was allegedly dealing performance-enhancing drugs to players. The bullpen is stacked, with Rafael Soriano, Drew Storen and Tyler Clippard combining to form one of the top late-inning combinations in the majors. Things appear to be lining up for another strong season in the nation's capital. It will take much more than one player for the Nationals to find their way back to the postseason or push further towards a World Series title. That's clear. But if you had to single out one player that you feel has to step up this season, who would you choose? Would it be Gonzalez, who will need to put the off-the-field distractions behind him and find a way to repeat his performance from the 2012 season? Would it be Stephen Strasburg, who finally won't have any limits on him this season and will be able to truly let loose for the first time since Tommy John surgery? Would it be Danny Espinosa, who will be playing with a torn rotator cuff but will attempt to cut down on the strikeouts and prove that he's the Nats' best option at second base? Would it be Span, who will be getting a new start in D.C. and whose presence essentially bumped Michael Morse out of town? How about Dan Haren, the new guy in the rotation? Soriano, who just got paid $28 million and knocked Storen out of the closer's role? Who do you see as the one guy who has to step up the most?