Afghan President Hamid Karzai began a four-day visit to Washington, D.C. on Monday.

The trip comes as NATO is preparing to launch an assault in southern Kandahar province. It will be Karzi's longest engagement with U.S. leaders since winning re-election last year.

Prior to his departure for the states, Karzai toured Bagram Air Field Saturday with top NATO commander Gen. Stanley McChrystal where he was briefed on Special Forces operations and he also visited with wounded troops.

Later he met with House Speaker Nancy Pelosi, D-Calif. and a congressional delegation in Kabul.

"The one word that emerged is the word that brings us here -- security," Pelosi said. "There are certain metrics that the Congress is looking to measure the progress being made in Afghanistan -- that is part of the purpose of this trip."

During his D.C. visit, Karzai and President Obama are expected to discuss the Afghan war and the future of that country when the war ends.

Karzai has said he believes Obama's announced troop withdrawal date next summer is problematic, putting a stopwatch on the war and giving an advantage to the Taliban.