The presidential candidate met officials and soldiers here this weekend at the start of a global tour.
The heightened political tensions between the two allies in the war on terror has prompted US presidential hopefuls to focus on improving Afghanistan strategy.
They seem to be moving from Iraq to Pakistan and Afghanistan.
Insurgents' ability to breach the post in Kunar Province is seen as a significant escalation in the fight.
The attack focuses international pressure on neighboring Pakistan, where many of the militants are said to be based.
Militants took control of a strategic district outside Kandahar. Afghan and foreign troops flew to the city in response.
An eight-month review by McClatchy newspapers says the US wrongfully imprisoned many suspected Al Qaeda terrorists.
President Hamid Karzai threatened Sunday to send troops to Pakistan to fight militants themselves.
Afghans sought help for its $50 billion five-year plan as donors met in Paris June 12.