Answer
Tsai Ing-wen was challenged by Lai Ching-te in the 2019 Democratic Progressive Party presidential primary. As the incumbent president, Tsai was seeking re-election for a second term. Lai, a former mayor of Tainan, was seen as a strong contender within the party. The primary was held on June 1, 2019, and Tsai ultimately emerged victorious, securing the party's nomination.