My analysis is this - Dem support is essentially in lockstep with Trump's disapproval rating. 54% of people don't support the wall. 54% of people don't approve of Trump. Doesn't matter what he does, 54% of the country isn't going to support him just because they hate him so much.
On the flip side, Trump's support is growing because it's becoming more and more clear that the Dems are being unreasonable. They all voted for this in the past and are playing hardball, trying to stop Trump from delivering his signature campaign promise. Undecided people are beginning to side with Trump because for $5 billion there's no reason to not build the wall.
Reality is that support isn't going to fall for the Dems. They're not gaining support, but they're not losing any either. Trump's best case is 46% support which would need every undecided person to side with him, which is unlikely. The Dems will hold out indefinitely because their base supports that stance, and the only way this is ending is with Trump declaring an emergency, triggering the Dems into calling Trump a tyrant who is going around Congress and possibly starting his impeachment.
Just my two cents.