Trump clearly isn't anything resembling a religious Christian, and likely stated he was Presbyterian because that was what he could get away with. However, because of the base he chose to cater to, and because of the tenuous establishment support he receives, his power is more directly derived from the people who vote for him and as such he's more beholden to their interests.
In contrast, the Democratic party has increasing disdain for Christianity as it shifts further towards progressivism as a dominant strategy. The only Trump analog in the Democratic party is an atheist Jew. There is no hope for your religious views to be represented in the Democratic party beyond lip service, especially if you're Christian, since-- on top of some of your views (e.g. being pro-life) being in contradiction to the Democratic platform-- you rank lower in relevance compared to, say, a Muslim, since they have more token power than you.
In short, regardless of what Trump himself believes, he's actively beholden to his voterbase and is more wont to act in their best interest. The Democratic party is less likely to do so, in comparison, and in fact has no strong incentive to do.