They can turn a huge win like the overturning of Roe into a loss by making abortion a central issue. In certain states banning abortion is a huge winner, in other states, it’s a huge loser.
The pro-marriage campaign in California won because they did not allow a fringe group to turn their campaign into a campaign against domestic partnerships, which was seen as not about protecting marriage but instead attacking gays and lesbians.
Most Americans are Christian but their religious sentiments are a mile wide and an inch deep. Democrats are careful to downplay anti-Christianism, Nancy Pelosi claims to be Catholic and her allies got her unbanned from Communion.
When Republicans defend Christians it is popular, when they attack non-Christians it is unpopular.
None if this is some big secret of political science or anything.
Of course ending immigration, legal and illegal, is hugely popular. But Republicans are not allowed to do that. That is the only real substantive issue.