From the Post ...

DeLay was determined to hang on to his seat at least through the primary, said Carl Forti, spokesman for the National Republican Congressional Committee. That was because he considered his three Republican challengers gadflies and traitors and he was determined to try to block them from succeeding him.

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An additional impetus for putting off the resignation until now was suggested by John Feehery, a former aide to DeLay and House Speaker J. Dennis Hastert (R-Ill.). "He needed to raise money for the defense fund. That was the bottom line," Feehery said. "He wanted to make sure he could take care of himself in the court of law." Under federal campaign rules, any reelection money a lawmaker raises can be used to pay legal fees stemming from official duties.

So the GOP candidate will be selected by party chairs. And a main reason for DeLay to stay in the race this long was to raise legal fees under the guise of raising money to run a political campaign.