1. They can leverage it to get some things they want.
2. They can show they are willing to compromise and be the "bigger man".
3. They can throw it in Trump's face in the election. If it doesn't work, they can claim that he held the government hostage for wasteful spending. They can also play up that they are serious about border security. So serious that they were willing to take a flier on it. I can't believe they would lose any of their base.