No American president has said it so clearly, even if the White House later backtracked: If China attacked Taiwan, the United States would defend the attacked militarily - they are obliged to do so.
That is not true;
by law, the US is “only” obliged to provide Taiwan with means of self-defense.
Indeed, arms deliveries have increased, as has military cooperation in general.
But this has now, whether unintentionally or not, extended Biden to an obligation to help - which would be a departure from the policy of "strategic ambiguity" - and thus raised Taiwan almost to the rank of Japan and South Korea: Both countries are America's security clients.
One could imagine that Biden's promise would be criticized by the leadership in Beijing.
But this is ultimately the result of China's most recent military intimidation attempts against Taiwan, which is why its leadership felt compelled to urge Washington for modern armaments to be delivered and for assistance in the worst-case scenario.
Experts do not think the situation is as explosive as it appears.
China has no interest in a military conquest of the democratically governed island, the majority of which want independence.
And Biden asserts that he does not want a cold war with China.
But “Taiwan” is and will remain the most explosive of all conflict points.