The Post Sports Live crew debate what manager Davey Johnson should do with the Nationals batting order to kickstart the offense. (Post Sports Live)

The second half of the Washington Nationals’ season begins Friday with a clear and simple mission: “Just being more consistent,” as Manager Davey Johnson put it. They can erase three and a half months of maddening mediocrity in a season of overwhelmingly high expectations with a strong final two and a half months. The Nationals, the defending National League East champions, have 67 games in which to make up a six-game deficit on the Atlanta Braves in the division standings.

For months, the Nationals have followed rousing wins with troubling losses. The sleepy offense, still among the lowest-scoring in baseball, has been perhaps the biggest culprit. Mistakes by the pitching staff, which has been strong but not as dominant as last season, have been magnified because of the tiny margins for error. Small gaffes and defensive errors have piled up. But now, except for a lingering back injury to starter Ross Detwiler, the Nationals are nearly whole again and expect to correct their mistakes.

“I don’t see why we can’t play a lot better in the second half,” starter Jordan Zimmermann said. “I think this little break is going to help a lot of guys with their mental approach.”

While the Nationals have dug themselves a hole, it is not insurmountable. Their ability to overcome it will hinge on several factors. Most of the team’s hitters are under even their career averages, and their 3.76 runs per game, the fourth-lowest total in the majors, is made worse by their habit of scoring in bunches one game, then slumping for several.

“We can’t score five runs one game and then one run the other game,” Zimmermann said. “And when we do get five runs, it always seems like the pitching staff and everyone, we give up five or six runs. We just need to be more consistent, and on the days we get five runs, don’t give up five runs. And on days we get two runs, we got to keep the team in there.”

The Post Sports Live crew makes the case for when and why Nationals Park should host the midsummer classic. (Post Sports Live)

Johnson, who has fiddled with the lineup several times, made his most drastic overhaul in the final game before the four-day all-star break.

Aiming to address the team’s horrid on-base percentage — only the Miami Marlins and the Houston Astros are worse than the Nationals’ .301 mark — Johnson moved leadoff hitter Denard Span to the seventh spot in the lineup and stacked two of the team’s best hitters, Bryce Harper and Anthony Rendon, atop the order. The change also jammed more right-handers between the team’s left-handed hitters.

“My left-handers, for some reason, their average against left-handed pitching was way down than what it normally is,” Johnson said. “Managers check that out, and so they’d go through a right-hander and get two left-handers. And then if they went in for the three-hole hitter, they’d go through the five-hole hitter. Changing it up, there’s a couple right-handers before the left-handers, makes it more difficult.”

The second half also will depend largely on the progress of the back end of the starting rotation. Dan Haren is in the midst of the worst season of his career with a 5.61 ERA and 4-10 record but has shown improvement in his two starts since returning from the disabled list. Detwiler, on the disabled list for the second time this season, has missed 40 days because of injuries and hasn’t been the same since his first one, an oblique strain.

Johnson believes in the team’s roster, and General Manager Mike Rizzo said a week before the all-star break that he didn’t anticipate making any “splashy” moves before the trade deadline in two weeks but noted that “it could always change.” If Detwiler’s health and Haren’s progress don’t continue to improve, the Nationals could be forced to make a move or rely on minor league replacements.

The three division winners and two wild-card teams make the playoffs, and over the past few seasons, the second-best non-division winner has finished with around 89 wins. To get there, the Nationals would need to finish the season 41-26, a .612 winning percentage. Last season, the Nationals’ best 67-game stretch was a 44-23 run through the summer.

But in a underperforming NL East, a run to the top of the division may be a more direct route. Since the Braves began the season 12-1, they’re 42-40. In that span, the Nationals are 40-42 and the Philadelphia Phillies are 42-41. The level of play in the division — one the features two teams with among the worst records in the league, the New York Mets and Miami Marlins — has been simply average. At 54-41, the Braves are only one game ahead of the Cincinnati Reds, the team currently in the second wild-card position.

“It’s a good thing we started off 11-1 or whatever we did, 12-1,” Braves closer Craig Kimbrel said.

“We played above .500 baseball, and no one has really ran away with it in this league,” Braves first baseman Freddie Freeman said. “With the Nationals, they’re only going to get better. They haven’t been playing like they normally should be playing.”

There may be hope at home. More than half of their remaining games — 36 of the 67 — will be held in Washington, where the Nationals are 27-18, for a .600 winning percentage. On the road, the Nationals are 21-29, for a .420 percentage. The Nationals’ remaining opponents have a combined winning percentage of .486, while the Braves’ opponents have a .474 winning percentage. The next 67 games will define the Nationals’ season.

“We’re an awfully good ballclub, and we just need to play like it,” Johnson said.