Today is the last day of Major League Soccer's secondary registration window, popularly known as the transfer window, which opened on July 8. That means that the juicy rumors involving MLS teams ridiculously linked with unobtainable players will sharply drop. D.C. United is still in need of a couple of different players, and in many other leagues the closing of the transfer window means that is your team until the next transfer window opens. However, Major League Soccer, as it is in many other respects, operates a little differently.
To get technical, the transfer window is the only time that a team can obtain the transfer certificate of a player who is under contract. That means that, unless the team acts today, they will not be adding any players who are currently under contract in any other league from around the world, whether on a full transfer or on a loan. However, that still leaves D.C. United (and all of the other MLS teams) with the full suite of player acquisition methods.
Specifically, any team can still sign players from overseas, as long as they are available on a free transfer, using the discovery signing mechanism. Each team has a list of 10 players across the world upon whom they have a discovery claim, and that team is the only one that has the right to try and sign that player (so as to prevent MLS teams from driving up prices by bidding against each other). This includes players from lower leagues in the United States, like how D.C. United signed Lewis Neal, or from abroad, like Cristian Fernandez. And, of course, all of MLS's special player acquisition methods are still in play: trades, waiver drafts, and weighted lotteries.
D.C. United needs to add a couple of players, but the closing of the transfer window does not mean that it is too late to do so. The hard date for any acquisitions is the roster freeze deadline, which is September 15. Given the current state of the team, what is highest on your shopping list: a forward, a midfielder, or a fullback?