Taiwan’s elections have returned the Democratic Progressive Party to power. Rolling over the incumbent Kuomintang (KMT) nationalists, the DPP won both the presidency and a legislative majority, giving it controls of both elective branches for the first time.

President-elect Tsai Ing-wen didn’t center her campaign on attacking the KMT policy of closer relations with China, focusing instead on Taiwan’s lagging economy, but neither did she reject the bedrock DPP platform of independence from China. Her rhetoric, including her...