The younger generation (like, born after 1980) of evangelicals, if they haven't left the church as many of them have, tends to be either less conservative across-the-board or, even if they are socially conservative, tend to recognize that service to the poor, protection of the environment, and compassion for the downtrodden are going to be more important than enacting abortion and gay marriage bans.
I would guess the 2020s at the earliest, though. I don't see evangelical Christianity having much currency at a national level for a while, certainly not with the Democratic Party, which is increasingly secular.