The Chinese military operates daily around Taiwan, activities that have continued while Cheng has been in China.
Taiwan’s opposition, which has a majority in parliament, has stalled government military spending plans, including an extra US$40 billion special defence budget which has provisions to buy US weapons and which Washington has backed.
Despite the lack of formal diplomatic ties, the US is Taiwan’s most important arms supplier and international backer.
Greene said that while the US supports dialogue, that cannot replace deterrence.
“I don’t think there is a conflict here, because if there is sufficient deterrence capability, it will lead to a more equal dialogue,” he added.
“There are three ways to resolve cross-strait differences: the first is dialogue, the second is coercion and the third is war. So if Taiwan can have sufficient deterrence capability, it can take the option of war off the table.”