Nationals outfielder Bryce Harper will become a free agent after the 2018 season and is reportedly seeking a historically huge deal worth at least $400 million. (Nick Wass/AP)

If the Nationals want to keep superstar Bryce Harper before he leaves as a free agent, they should take a lesson from the Redskins, who are still at a contract stalemate with their one-year rental, franchise-tagged quarterback.

The baseball club should treat Harper the opposite of how their neighbors in Ashburn are treating Kirk Cousins.

According to a USA Today report from last year’s winter meetings, Harper is seeking a deal that would be worth at least $400 million over 10 years or more.

Although the 2015 NL MVP hasnít stated these demands publicly, he appears set to test the market as a free agent after the 2018 season and become the highest paid player in baseball at age 26, unless the Nationals intervene.

Owner Ted Lerner and general manager Mike Rizzo should offer Harper a $425 million deal right now. Considering that the largest active contract belongs to the Marlins’ Giancarlo Stanton, who’s pulling in $325 million over 13 years, that might sound crazy. But having Harper, who hit .354 with a 1.162 OPS and 13 RBIs in his first 13 games this season, for the long term is worth a king’s ransom.

The last thing the Nats should do is lowball Harper. The Redskins have spent the past two offseasons shortchanging Cousins, and it’s about to cost them dearly next year. At $34 million, the one-year franchise tag would be too expensive to use on Cousins a third straight time. If team president Bruce Allen tries that move again, he should be tarred, feathered and kicked out of town.

The Redskins have choked on their pride, but the Nats need to swallow theirs.

Cousins’ exit would hurt Washington’s football team, but it wouldn’t devastate the city like a Harper exit. If Cousins leaves, half of Redskins fans won’t care. They’re still bitter over Robert Griffin III failing, and never embraced his replacement. Cousins is simply a good quarterback. Harper has flashed Hall of Fame potential.

Harper is unquestionably the face of the Nationals. There’s no replacing him. Trea Turner has provided hope for the future, but Harper is the still the one everyone stops to watch. He’s the one who wins games at the end. (See Sunday, when he hit a walk-off homer in the ninth inning. Or last Friday, when he slid into home plate on Daniel Murphy’s game-winning double in the 10th.)

In 2016, the Redskins wanted one more season to assure themselves that Cousins was the real deal. Maybe the Nats are doing the same thing with Harper after a sub-par effort last year in which he hit a career low .243, but still smacked 24 homers. He batted .330 with 42 homers in 2015 — his MVP year.

Maybe Harper and agent Scott Boras are holding out for a historic payday, but if his status has anything to do with hesitation on the Nationals’ part, they need to stop waiting.

When the Redskins dragged their feet, Cousins tore through the team’s record book for the second year in a row. Now he’ll make at least $4 million more than he should this season.

This year, Harper, 24, already looks like the next Mickey Mantle. The Nats overpaid to keep pitcher Stephen Strasburg (seven years, $175 million), and he doesn’t offer nearly the impact of an everyday slugger like Harper.

If the Nationals need to charge 50 cents more per beer to cover Harper’s deal, then fans will drink to that.

Read more columns from Rick Snider:

The Redskins have bad luck with first-round running backs. They should draft McCaffrey anyway.

Nats need to embrace the grind over the next 6 months

Divorce with Scot McCloughan doesn’t doom the Redskins’ draft

The Redskins have been frugal and practical in free agency

Five domino effects from the Redskins tagging Kirk Cousins