[7] He was named the Democratic Progressive Party candidate for Taichung 1 in 2008, and lost to Tsai Chin-lung in the January legislative elections.

[10][11] After leaving politics, Tsai continued to advocate for stronger Taiwan–United States relations and has led the Taiwan United Nations Alliance.

[15] In November 2007, while Tsai was vice defense minister, Aerospace Industrial Development Corporation won a bid to produce equipment for the Republic of China Armed Forces.

Kuomintang legislator Tsai Chin-lung had reviewed military equipment, found the specifications to violate the contract terms, and ordered AIDC to suspend production.

[16] The Taipei District Court ruled in September 2011 that the claims against Tsai Chin-lung were unsubstantiated and ordered all four accusers to publish a public apology.