* Nike's drop after rating cut weighs most on S&P, Dow
* Herbalife jumps as board announces stock buyback
* Dow off 0.04 pct, S&P up 0.03 pct, Nasdaq 0.06 pct (Updates to open)
Aug 21 (Reuters) - U.S. stocks opened little changed on Monday, with some measure of calm returning after a turbulent two weeks during which turmoil in the White House and simmering tensions between the United States and North Korea roiled the markets.
Last week, President Donald Trump fired chief strategist Steve Bannon and disbanded some business councils among other political maneuvers, while there was also speculation about the possible departure of National Economic Council Director Gary Cohn.
The unrest in the White House again led to investors' concerns about the Trump administration's ability to implement its pro-growth agenda.
While the benchmark S&P 500 index is still up 13.4 percent since the election, it had fallen 2.1 percent in the last two weeks. That's the most since the two weeks before the election.
Part of the decline was due to escalating tensions between the United States and North Korea. While that has eased slightly in the past few days, South Korean and U.S. forces began computer-simulated military exercises on Monday.
"Investors are taking a step back and evaluating the move lower", said Andre Bakhos, managing director at Janlyn Capital in Bernardsville, New Jersey
"They are not sure if it's a beginning of the end of the bull run we've had or if it's a buying opportunity", Bakhos said.
At 9:39 a.m. ET (1339 GMT), the Dow Jones Industrial Average was down 8.78 points, or 0.04 percent, at 21,665.73 and the S&P 500 was up 0.74 points, or 0.03 percent, at 2,426.29.
The Nasdaq Composite was up 3.94 points, or 0.06 percent, at 6,220.47.
Seven of the 11 major S&P indexes were higher, with the telecom sector's 0.35 percent rise leading the gainers.
Among stocks, Nike's shares dropped 2.7 percent to $53.45, weighing the most on the S&P and the Dow, after Jefferies downgraded the stock and also cut its price target.
Herbalife was up 8.96 percent at $67.50 after the nutritional supplement maker said it would buy back $600 million of shares after ending talks to be taken private.
NYSE-listed shares of Fiat Chrysler were up 4.81 percent at $13.18 after China's Great Wall Motor said it was interested in bidding for the carmaker.
Declining issues outnumbered advancers on the NYSE by 1,268 to 1,201. On the Nasdaq, 1,302 issues fell and 960 advanced. (Reporting by Sruthi Shankar in Bengaluru; Editing by Savio D'Souza)