Hsieh was frequently considered to be a leading contender for the DPP nomination in the 2008 presidential election, and formally announced his intention to run in the election on 16 February 2007. Hsieh was the second to formally declared candidacy, after the Kuomintang's Ma Ying-jeou did so three days prior. Hsieh won 45% of the vote in the Democratic Progressive Party primary. A scheduled straw poll was cancelled after his three primary opponents all conceded defeat, and Hsieh was declared the DPP nominee. In July 2007, Hsieh visited the United States, branding it "the journey of Love and Trust" (). In September 2007, Hsieh openly declared that he was running for the presidency of the State of Taiwan (), saying that "recognizourselves (the Taiwanese people) as a nation first and then fight[ing for what we want during negotiations with other countries" is important. As a result of the Kuomintang's allegations of graft against Hsieh, prosecutors began an investigation of him in 2007. The investigation ended in September, when it was announced that Hsieh would not be charged with wrongdoing.