sitting

ここのsittingは文脈からも推測できると思いますが、「座っている」から派生し、「現役の、就任している」という意味を表します。sittingは他にも英国用法で、「議会が開会中の」という用法もあります。（UG）

In Myanmar, Obama lauds courage of Aung San Suu Kyi

(CNN) -- Barack Obama met with Nobel Peace Prize winner Aung San Suu Kyi at her home in Myanmar on Monday, lauding her "courage and determination" during a historic visit to the once repressive and secretive country.

The first sitting U.S. president to visit Myanmar, Obama urged its leaders, who have embarked on a series of far-reaching political and economic reforms since 2011, not to extinguish the "flickers of progress that we have seen."

Obama said that his visit to the lakeside villa where the pro-democracy icon spent years under house arrest marked a new chapter between the two countries.

"Here, through so many difficult years, is where she has displayed such unbreakable courage and determination," Obama told reporters, while standing side by side with his fellow Nobel peace laureate. "It is here where she showed that human freedom and human dignity cannot be denied."

http://edition.cnn.com/2012/11/19/politics/obama-asia-trip/index.html?hpt=hp_c1