Update (3/30): Miya's follow-up blog entry:
"I believe that if we don't get my re-election numbers into the 60s percentage, then every Republican in Harris County could lose." Culberson says that's why the Democratic party is running such a rich guy, basically to beat him down ... and bring the Repub party along. In essence, he says he can still win his seat, while Harris County repubs lose all of theirs. He also says that if his winning percentage isn't high enough, John Cornyn could lose his Senate seat. So basically, in his view, the survival of the Republican ticket depends on re-electing him ... and thus, donating money to make him competitive against Skelly.
Update II: Charles piles on.