It is important to distinguish between "faithful" Catholics and mere Catholic identifiers in the electorate. Many surveys fail to make that distinction and thereby lump together in the same category both regular church-attenders and those who identify culturally as Catholics but do not worship. Surveys that make such distinctions show that Bush has strong support among "faithful" Catholics, suggesting that his appeals and issue stands are helping him with those Catholics who develop political loyalties based on their faith. Bush's troubles are with the much larger population of Catholic identifiers who are not politically persuaded by Church positions on issues.
The key for the president is to mobilize the enthusiasm of churchgoing Catholics while minimizing his losing margin among Catholic identifiers who do not go to church.