As Donald Trump seeks progress with North Korea at a second summit, the United States (US) has a series of cards it can play including easing sanctions, signing a peace declaration or even pulling troops from South Korea.After the historic handshake between the US president and North Korean leader Kim Jong-un in Singapore in June, Washington policymakers are adamant on the need for tangible concessions by Pyongyang on its nuclear program at the sequel meeting, which Trump says will take place