Only few members of the US Men's National Team come from the MLS ranks, because few MLS players have the skills necessary to thrive in international play. That's not to say that American men can't succeed in international soccer. The most successful active (male) US soccer player, Clint Dempsey, has been a top player at Fulham, and US MNT goalkeeper Tim Howard has played for Everton for years.
(For non-soccer-savvy readers, neither Everton nor Fulham is a powerhouse of the Premiership, but both have been pretty good teams by EPL standards for the last few years. Consider Everton to be the equivalent of the Chicago Bears or thereabouts: A club with a rich history that consistently does okay but not great, and whose last sustained success came in the 80s. Fulham, by contrast, is more like the Cleveland Browns. Perennially middling, gone entirely from the top-flight league for a span in the 90s, but back in moderate contention.)
Editor's note -- for those who don't follow American football, Mr. Kiley has just paid Fulham a grievous insult.
Since the MLS season is offset from the soccer season of the ENTIRE PLANET*, there's a two-month window during which MLS players can play for international clubs. In 2010 and 2012, Donovan has been loaned to Everton for several weeks during that window. In each of those two years he's received an Everton "player of the month" award. Near the end of the last home game of Donovan's 2010 Everton stint, fans at the stadium chanted "U-S-A" to credit his excellent play.
For the betterment of his own skills, and for the sake of the US national soccer program, Donovan should remain with Everton.
A player really only improves when he faces opposition that is comparable to his own talents. There are a few good teams in Major League Soccer. Donovan's championship LA Galaxy is chief among those. By comparison to the English Premier League, the rest of MLS is the soccer equivalent of the Lehigh Valley Iron Pigs.
There's something to be said for keeping the American game's biggest star playing within the United States. It certainly helps raise the visibility of the league in general, and helps the league be taken more seriously. But the best thing that can be done for American soccer is for the men's national team to have consistent success in the World Cup. Once that happens, the MLS will be seen as more than just a second-flight league. And until that happens, the best American players need to face the world's best competition.
* Don't get me started.