The unenviable job of policing the relationship between Taiwan and its strongest ally, the United States, belongs to Zhou Mingwei, Vice-Minister of Beijing's Taiwan Affairs Office. The position is regarded as the toughest in the department. Miscalculations could result in war. He has earned top marks since his appointment two years ago. 'He is very smart and sharp,' said one senior cross-straits expert in Washington. Even a Taiwanese security expert conceded: 'He performs very well. He speaks the Washington language.' Schooled in the art of diplomacy, Mr Zhou speaks fluent English after spending long periods in the US, including two years as a Fulbright scholar at Harvard University's John F. Kennedy School of Government. Before joining the Taiwan Affairs Office he was Shanghai's chief of foreign affairs. Mr Zhou's skills have been tested by the White House's cooling relations with Beijing. This year he has travelled to the US twice to urge Washington's biggest Taiwan supporters, including Vice-President Dick Cheney, not to interfere in China's affairs. Experts say Mr Zhou made an impact. But his biggest obstacle is that Washington feels Taipei has no obligation to accept the 'One China' principle before dialogue with Beijing opens. 'He really impressed Americans in his visits to Washington. However, they discovered that his core ideology is the same [as Beijing's],' said Professor Lin Chong-Pin, a mainland expert at Taiwan's National Sun Yat-sen University.