A week before the presidential election, incumbent President Chen Shui-bian vowed to quit if Ma could provide legal documents of the invalidation of his green card. The DPP presidential candidate Frank Hsieh also said that he was willing to withdraw from the race if Ma could prove, using official documents, that his green card was invalidated twenty years ago. Ma responded the next day to the president that he should work on improving Taiwan's economy instead of caring about the election so much; earlier, Ma also provided copies of US non-immigrant visas issued to him during the 1980s and 1990s, claiming the card was invalid, as such visas are not issued to green card holders.