The
U.S. used to station forces in Taiwan BEFORE Nixon and Kissinger
reestablished of diplomatic relations with the PRC.
As part of this process the U.S. formally agreed (in the Joint
Communiqué on the Establishment of Diplomatic Relations of 1979) to
"recognize the Government of the People's Republic of China as the sole
legal Government of China" and declared its intention to only "maintain
cultural, commercial, and other unofficial relations with the people of
Taiwan".
The termination of official relations with "the people of Taiwan" and
the agreement by the U.S. to limit the relationship with them to
"cultural, commercial, and other unofficial relations" implied a
cessation of official U.S. military presence on the island. And as a
matter of fact the U.S. completed the withdrawal of its military
personnel and dismantled its military installations in Taiwan by April
1979.
So putting troops back on Taiwan, and especially so close to the Chinese
mainland, makes a complete mockery of the agreement between the U.S.
and the PRC, and challenges 45 years of status quo.