Though they share similar beliefs and political ideologies, cooperation between the DPP and Taiwan Solidarity Union (TSU) is not guaranteed to be smooth, political observers say.
One of the main issues that could come between the two pro-Taiwan parties is the sharing of power, analysts say.
If the DPP doesn't handle the relationship with its younger sister carefully, the party runs the risk of losing the backing of its closest ideological ally.
"In Taiwan, partisan coalitions based merely on a similarity in beliefs would be very shaky, as Taiwan's politics are not controlled by parties, but by local factions," said David Huang (
"Parties are no more than an election machine. Once the election is over, each individual politician will be his own master."
Huang said that while former president Lee Teng-hui (李登輝) was a main factor in the TSU's strong showing in the polls earlier this month, the importance of local factions should not be underestimated.
As a result, cooperation between the DPP and TSU cannot rely solely on agreements reached by the two parties' high-ranking officials.
The DPP must also be ready to provide the TSU with resources and power, so that TSU lawmakers are willing to collaborate, Huang said.
The four-month-old pro-Taiwan party garnered 13 seats in this month's legislative elections -- largely as a result of Lee's support.
Lee founded the party to help bring stability to the unruly legislature. Because of the DPP and TSU's support of pro-localization policies, the two are natural allies.
But cooperation between the two has not always been smooth.
During the election campaign, for example, DPP members complained loudly that the TSU would siphon away voters from the party.
DPP Chairman Frank Hsieh (謝長廷) once ridiculed the TSU's nominees as "second-rate."
Distrust between the two continued after the polls. DPP officials were upset because the TSU early in the election aftermath pledged support for Wang Jin-pyng's (王金平) bid to seek re-election as legislative speaker.
DPP members also say that Lee has been stealing the limelight from President Chen Shui-bian (
With the constant bickering, analysts say there's no way the TSU will "unconditionally" support the DPP government. The DPP must learn "the art of power-sharing," they say.
And while many of the disputes between the DPP and TSU have been over power, analysts say there are areas where the two differ on policy, the main one being cross-strait relations.
Political watchers say the two parties need to step up negotiations to iron out the disparities.
"In terms of the cross-strait issues, Lee and Chen hold rather disparate perspectives," said Philip Yang (楊永明), associate professor of political science at National Taiwan University.
"While Chen has softened his stance by ... relaxing restrictions on business investment in China, Lee remains a hard-liner," Yang said.
China could also view the DPP's alliance with the TSU with suspicion, the professor said.
"Chen has to know how to skillfully deal with imminent problems. Domestically, Lee serves as his best partner. But how Beijing will react to the DPP's cooperation with Lee -- China's most-hated Taiwanese politician -- should be closely watched."
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