If you're looking for legitimate reasons for hope that the Nationals can contend, here's one: the NL is full of teams with big problems.
The Cardinals and Phillies are solid, and the Giants' pitching will keep them in it, but the other teams expected to win this year are all struggling. The Braves can't hit at all. I still think the Dodgers will be in it till the end, but the back-end of their rotation is weak, and all you need to know about their bullpen is that former National Ramon Ortiz has the most relief innings on the team. Colorado has been better than their record shows, but in part because of injuries, their rotation is suspect after Ubaldo Jimenez.
What about the surprise teams? Can any of them keep it up? The Padres are 19-12, but they're the same Adrian Gonzalez and everyone else team that they've been for the last few years. The Mets are clearly set up for a major fall.
The Reds and Marlins were popular sleeper picks going into the season. The Brewers have some real strengths. But all those teams have major flaws too.
So when you add it all up, why can't these Nationals keep up with those teams. They'd get destroyed in the AL East, but in this NL, If they can win half their games, they're going to have a good shot of staying in the race until the last week or two of the season.