Dallas Keuchel is among the big-name free agent pitchers who might interest the Nationals this winter. (Orlin Wagner/Associated Press)

The correlation between the performance of the Washington Nationals' starting rotation and the success of the team as a whole is conclusive: When their rotation ranks among the league’s elite, the Nationals make the playoffs. When it lulls into mediocrity, they do not. The rotation slid into to mediocrity in 2018. So did the Nationals.

So as Mike Rizzo and his staff drew up their plans for this complicated offseason, they had little soul-searching to do. The best fix for this team after its disappointing season, and the best predictor of its success down the road, is bolstering the rotation.

“Starting pitcher is the driver to me,” Rizzo said at last week’s General Managers' meetings. “ . . . We’ve built our clubs based on having a guy in the middle of the diamond who gives us a chance to win every day.”

Max Scherzer finished second in the Cy Young voting. He is their ace. Stephen Strasburg’s velocity dropped late last season, and he continued to battle health issues. He is supposed to be an ace. Gio Gonzalez is gone. Tanner Roark has been inconsistent. Joe Ross seems to be a reliable back-end option, but neither Erick Fedde nor Jefry Rodriguez have established themselves as such. The Nationals need more starting pitching, and they need front-end types both to help their cause in 2019 and to stabilize the rotation as Scherzer and Strasburg age.

The free agent market yields plenty of options. Left-hander Patrick Corbin seems likely to earn the biggest payday of any free agent starter, and the Nationals will almost certainly make that call. They also think highly of lefty Dallas Keuchel, whose groundball-inducing skills rank among the league’s best. He would serve as a Gio Gonzalez-esque complement to Scherzer and Strasburg at the top. Right-hander Nathan Eovaldi strengthened his credentials with a resurgent playoff performance. Veteran righty Charlie Morton also is a free agent and has found good velocity and increased effectiveness later in his career.

“We’ll keep all of our avenues open,” Rizzo said. “We recognize who [the top free agents] are, and we’ve never been afraid to step out and sign a free agent or make a trade, and that’s been our plan going forward.”

The trade market could yield far more interesting possibilities. For example, the Arizona Diamondbacks are reportedly willing to part with key pieces. Rizzo and his staff have always thought highly of veteran right-hander Zack Greinke, who is 35. He is also making $34 million in average annual value, a percentage of which the Nationals could probably shoulder to lessen the prospect return needed. Greinke pitched to a 3.21 ERA in 33 starts last season. Also on Arizona’s staff is left-hander Robbie Ray, a one-time Nationals draft pick. Rizzo often explores reunions with his own.

The Cleveland Indians are reportedly open to dealing some of their starters, including two-time Cy Young Award winner Corey Kluber. The Toronto Blue Jays and Seattle Mariners also are open to deals. Barring a trade for — say, a catcher — that empties their system, the Nationals have the prospects to deal for an elite starter if they see an opening. They will almost certainly look for one.

Middle-of-the-road options exist, too. Less decorated pitchers such as J.A. Happ, Matt Harvey, Drew Pomeranz, Garrett Richards and others are available in free agency. But Rizzo has never been one to patch his rotation from back to front. From the time he dealt four players for Gio Gonzalez before the 2012 season, Rizzo’s deals for starters have been for front-line types such as (at the time) Doug Fister and a free agent push for Scherzer. If he makes a big deal, he often gets a big name. Sometimes, as with Scherzer, he does not even seem to have a glaring need.

This winter, he does have a glaring need. Regardless of what Bryce Harper decides, the Nationals are a catcher away from a highly competitive major league lineup as things stand now. But history suggests a lineup, alone, has never been enough.

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