He's here to make the team, which sets up one of the most intriguing issues in all of spring training.
"I don't really need to show them anything," Harper said. "I just need to come out here and play my game, play hard, just try to interact with all the guys, let them get to know me. Davey has seen me play before. They've all seen me play. They know what I'm about. They know what I can do."
The Nationals seem to be of two mindsets. There's general manager Mike Rizzo, who speaks cautiously of rushing Harper to the majors too quickly. Then there's Johnson, who may be the oldest manager in the majors at 69 but isn't against giving Harper a legitimate chance to earn a starting job.
Back in the 1980s, when he was managing the New York Mets, Johnson had a bright young pitching prospect named Dwight Gooden. He was only 19, but the manager felt he was ready to pitch in the big leagues. The front office wanted to give the kid another year in the minors, but Johnson lobbied hard and got his way. Turns out, he was right on the mark. Gooden won 17 games and was named to the All-Star team.
"I've got an open mind about everybody in this camp," Johnson said. "He has the highest ceiling just off what I've seen, but whether it plays out that way or not, time will tell. I'm not locked in on anybody."
Johnson intends to give Harper every chance to make the team, starting with the very first round of live pitching Sunday. He'll be placed in one of the main hitting groups and could be matched against Washington's other phenom, Stephen Strasburg. When the Grapefruit League games begin, look for Harper to get most of his playing time in the early innings, so he'll be going against big league pitchers rather than end-of-the-roster guys who have no chance to make the team.
"I'm going to compare apples to apples," Johnson said. "The talent and makeup is off the charts. That should lead to quality performances."
Rizzo is a bit more restrained.
"It's extremely tough for a 19-year-old to make it," the GM said. "There's not that many with the ability level to play in the big leagues. But we're going to keep an open mind to it. If we feel he's ready developmentally to handle the rigors of a major league season, we'll be open-minded about it.
"The talent level is definitely there," Rizzo added. "But there's an experience level that needs to be reached, an emotional level, the rigors of the everydayness of the majors leagues, that's all something we have to think about."
Harper seems to be working hard to fit in. During batting practice Saturday, he kept to himself but glanced over a few times at Ryan Zimmerman and Jayson Werth, grinning a bit as the veterans cut up among themselves.
But there are times when he carries himself as a star. At the end of the two-hour workout, he lingered on the field while the other rookies made the quarter-mile walk from the practice fields to the main stadium. Then, with several dozen fans lurking around in hopes of grabbing an autograph, Harper spotted an equipment cart, hopped aboard and sped back to the clubhouse without doling out any signatures.
"He's been pretty professional with it," said Adam LaRoche, the Nationals' first baseman. "He kind of keeps to himself and does his own thing. That's kind of the thing with the rookies: to be seen and not heard."
From LaRoche's perspective, the key to determining whether Harper makes the team this year is how he deals with failure, not success.
"If he can handle it and recover from it, he's probably ready," LaRoche said. "If he can't do that yet, then he's probably not. The talent is there. You know it's there. They know he can hit at any level. But can he handle the first funk he goes in? When you've got 20 media standing in front of you, wondering why you're hitting (.120)? Do you let that go to your head and screw up the rest to the year? Or can you stop it and get after it?"