As Afghanistan's second presidential election loomed in early 2009, President Hamid Karzai described his once-genial relationship with the U.S. as a "gentle wrestling match" that he hoped to win.

Exactly four years later, another Afghan election is nearing, and his match with Washington has become far more grueling — a sometimes blistering fight that Karzai has waged this month with a flurry of public statements and speeches. But this time, the invective is bolder and the stakes are higher, as Karzai is interfering with U.S. President Barack Obama's own political aims of ending the Afghan war smoothly.

In recent weeks, Karzai has accused the U.S. of collaborating with the Taliban, torturing Afghan civilians, kidnapping university students and deliberately violating his country's sovereignty by attempting to undermine its institutions.