IT SEEMS LIKE ONLY A few months ago that commentators were blithely babbling about how much relations between Beijing and Washington had improved since the start of the Bush administration, which was marred by China's downing of an American EP-3 surveillance plane and the detention of its crew. The conventional wisdom was that the war on terrorism had united the United States and China against a common enemy. This rosy scenario is, unfortunately, being undermined almost daily by Beijing's actions.

Consider what the Chinese Communist leadership has done just in the past year: It passed an "Anti-Secession Law" asserting its legal authority to employ "nonpeaceful means" against Taiwan should the island democracy take any steps toward independence. Along with Russia, it pressured Central Asian republics to kick out U.S. bases being used in the war on terrorism; U.S. forces are now vacating a supply hub in Uzbekistan. In return for this, China has offered no useful assistance whatsoever in the fight against Islamist fanatics. Instead it held its first-ever military exercise with Russia--an exercise transparently focused on combating the United States--and agreed to purchase billions of dollars in Russian military equipment. And it continued its breakneck military buildup, which is focused on the kinds of weapons--especially missiles and submarines--needed to stymie U.S. efforts to protect Taiwan.

It also continued its massive campaign of industrial espionage intended to steal U.S. military and technological secrets. It has made some progress in protecting intellectual property but still tolerates massive copying of proprietary material that costs U.S.

Moreover, it did not reprimand, much less fire, a major general in the People's Liberation Army who publicly threatened to nuke "hundreds" of U.S. cities if the United States came to Taiwan's defense. It continued cozying up to odious regimes in places like Sudan, Venezuela, and Iran, whose oil it covets. It has also made clear that it will not cooperate in the U.N. Security Council or elsewhere in taking firm steps against nuclear proliferation by Iran and North Korea. Rather than using its considerable leverage on Pyongyang, it has brokered a replay of the 1994 Agreed Framework under which Kim Jong Il gets more foreign aid--including a "civilian nuclear reactor"--in return for the promise, but not the reality, of nuclear disarmament. Beijing also organized demonstrations, which turned into riots, aimed at America's foremost Asian ally, Japan. And, just to rub it in, China has pressed to exclude the United States from an East Asia summit meeting in Malaysia in December.

To be sure, the blame for greater Sino-American friction does not rest entirely with Beijing. The Bush administration and Congress, at the bidding of domestic protectionist lobbies, have done their best to irritate China through pressure to revalue its currency and limit its exports to the United States. And, despite all these tensions, there are also some signs of cross-Pacific friendship--China did agree this year to revalue its currency slightly and to buy $5 billion worth of aircraft from Boeing rather than its European rival. But there is little doubt that the Sino-American relationship is more strained today than at any time since 2001, the year of the EP-3 incident, mostly because of greater Chinese assertiveness and increased willingness to challenge American "hegemonism."